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Research Topic: Which Battery Will Do?

 
Last updated:  

Overview & Terms
8 March 2012
Single Use
7 January 2016
Rechargeable
1 September 2013
Battery Analyser
21 November 2017
Battery Shopping
12 May 2018

Recommended Batteries
for Particular Uses

16 May 2014

 

Original article by Ian Mander, 22 July 2002

Single Use Test
6 November 2007
Rechargeable Test
15 November 2018
Test Procedure
4 June 2011
Button and Coin Cell Shopping
12 October 2018
More Info & Links
29 February 2012
  LSD Shootout
7 January 2016
When Battery Testing
Goes Bad –
Consumer Magazine

2 October 2017
Battery Holder Shopping
3 December 2017

When Battery Testing Goes Bad – Consumer Magazine

First posted 12 October 2011, updated 27 November 2011, 19 January 2013, 1 September 2013, 7 January 2016, 11 September 2016, 2 October 2017.

The point of a good test is to allow buyers to make an informed decision about what is best to buy. Consumer has failed to do this. In its October 2011 issue Consumer published a rechargeable battery test titled "On and on ..." by Paul Smith which drew flawed conclusions from the report's own test data about which NiMH batteries are the best. This resulted in poor quality batteries being recommended by Consumer.

I've taken a closer look at Consumer's results for two of the batteries included in their test – the Energizer Recharge and the Sanyo Eneloop – and drawn my own conclusions about what Consumer's results actually mean. I'll also explain how they should actually have tested certain battery characteristics such as self discharge.

Faulty Understanding of How Batteries Work

The first problem with the Consumer report is the Consistency score, which accounts for 30% of the total score for each battery. Their idea of "consistency" for a battery is "measured by the amount of running-time the battery loses over its life. A high score is good." (Italics in original.)

Actually no. A high score is bad.

Consumer's test procedure defined the end of life of their batteries to be when "the battery capacity is reduced to 50 percent of its starting charge", by which they probably mean 50% of its initial capacity. That's OK – the test has to finish sometime – but the article claims that the Energizer Recharge was "the most consistent performer, losing only 21 percent of its running-time by the end of its life."

How is it possible for a battery to lose 50% of its capacity but only 21% of its runtime?

Clearly the discharge did not involve a constant current discharge, which would always give 50% runtime for 50% capacity. This is an immediate concern with the test method because it's the simplest way of measuring capacity. If the discharge current is fixed, the capacity can be found simply by measuring the time taken for a battery to discharge down to a pre-selected termination voltage (normally 0.9 V). Any other method requires recording the battery voltage as the battery is discharged through a fixed resistance then calculating the capacity from the resulting data, or by measuring the current as the battery discharges and integrating over time to find the capacity.

The simplest way to explain the Energizer Recharge result is if the test involved a constant resistance load, for example, by using a 1 Ω resistor. The current the resistor draws will depend on the voltage of the battery according to Ohm's Law, V = I * R (or I = V / R). Because the resistor is 1 Ω, V = I. The battery condition deteriorates during the testing, so at the end of the test the battery cannot deliver the same voltage as when it was new. This is because the battery's internal resistance increases, meaning any load placed on the battery sees a lower voltage because some of the battery's voltage has already been dropped across the battery's increased internal resistance. Less voltage means less current, and because the current has decreased, runtime is extended compared with what it would have been with a constant current test. A standard resistor across the battery terminals allows the calculation of capacity using a voltage logger and Ohm's Law.

Ideally a battery's voltage would not deteriorate at all over its usable life, and like a constant current discharge it would also always give 50% runtime for 50% capacity for any given resistive load. It would always perform like a new battery except for not lasting as long. Unfortunately Consumer would give that ideal battery only 5/10 for Consistency.

In other words, Consumer's Consistency figure is actually a Crappiness figure. The higher the Consistency figure the worse a battery performed, because the extension in runtime is a direct result of an undesirable lower voltage.

Practical Consequences of Crappy Batteries

  • Electronic devices that are particularly voltage sensitive such as digital cameras possibly won't even turn on because the batteries don't hold a high enough voltage.

  • Even if a device does turn on, its performance is likely to be impaired. For example, a digital camera will take significantly longer to charge its flash, it may turn off as soon as you try to take a flash photo, and/or its screen may be disabled; a walkie talkie may be unable to transmit (the walkie talkie may turn off when you try); incandescent torches will be much dimmer (and operate less efficiently); radio controlled cars will crawl instead of honking along.

  • Many battery chargers will reject the batteries due to their high internal resistance. This causes a lot of frustration, especially if few cycles have been completed. This could significantly reduce the actual number of cycles achievable by several of the batteries Consumer tested!

  • Battery chargers that do not reject old batteries are likely to miss termination – they don't stop charging when they should because the very slight drop in a bad battery's voltage that indicates it's full is too small to detect. This causes very hot batteries which further damages the batteries (internally and sometimes the label externally as well).

If runtime at the cost of voltage really was a desirable thing then all batteries would have a resistor connected in series. It would lower the voltage available to the device using the battery, especially at high current (because there would be voltage drop across the resistor), but that would reduce current and thus extend runtime. Imagine a torch being run on this sort of battery – it would last longer but would never give adequate light. With its Consistency score Paul Smith and Consumer would have us believe this would be a good thing.

How Good Are the Energizer Recharge Batteries Really?

From Consumer's results the Energizer Recharge got 2455 mAh at the start of the test with an initial runtime of 138 minutes, meaning an average 1.07 A discharge rate. 50% capacity at the end of the test, or 1227 mAh, with a 21% lower runtime, or 109 minutes, means an average of just 0.675 A. The significantly lower average discharge rate at the end of the test is a direct consequence of the lower voltage that the battery can maintain in its aged state.

This is not a battery in a good condition. Any normal capacity test would have found it to have abysmally low capacity because of its large voltage sag dropping its voltage under load to less than the normal 0.9 V termination voltage very quickly. It would have been rejected by many smart chargers long before the test was terminated because of its greatly increased internal resistance.

Compare that with the Sanyo Eneloop. The Eneloop got 2068 mAh at the start of the test with an initial runtime of 111 minutes, which works out to an average 1.12A discharge current. 50% or 1034 mAh at the end of the test works out to an average 0.93 A at the end of the test. This seems pretty good for a battery so well tested that it only has 50% of its original capacity left. Whether it was good enough to still use in the real world would probably depend on the exact purpose. Either way, those average discharge currents are better and considerably better, respectively, than the Energizer Recharge.

Battery Initial
Capacity & Runtime
Initial
Average Current
Final
Capacity & Runtime
Final
Average Current
Final Current
% of Initial Current
Energizer Recharge 2455 mAh
138 min
1.07 A 1227 mAh
109  min
0.675 A 63%
Sanyo Eneloop 2068 mAh
111 min
1.12 A 1034 mAh
67 min
0.93 A 83%

The last column in this table, Final Current % of Initial Current, gives a better idea of the state of the batteries than the figures Consumer presented, and are roughly the opposite of Consumer's Crappiness figures. Instead of doing these calculations, the Crappiness figures can be corrected directly using 50/Crappiness.

What difference does it make to Consumer's Overall Scores using these corrected figures contributing that 30% of the total score instead of Consumer's bogus Crappiness figures? The Energizer and Sanyo are no longer running neck and neck.

Battery Consistency/
Crappiness
Original
Overall Score
Corrected
Consistency
Corrected
Overall Score
Energizer Recharge 8.0 69 6.3 64
Sanyo Eneloop 6.0 70 8.3 77

The Energizer Recharge got the lowest Corrected Consistency score (the highest Crappiness score) in the test but was summarised by Consumer as having "No obvious bad points." Clearly Consumer does not understand what a bad battery looks like.

Most of the low self discharge (LSD) batteries in Consumer's test are pretty consistent – as indicated by low Crappiness scores – so were incorrectly rated too low in their Overall Score. Clearly, the more consistent batteries are the ones that suffered less voltage loss and are thus able to maintain a higher average current over the battery's life.

This is a very serious failing of the Consumer test.

Runtime and Cycle Life

Runtime is certainly something to take into consideration with a rechargeable battery, but how justified is a simple comparison of runtime retention, especially when it's over the life of batteries that achieve considerably different numbers of cycles? For example, is the Energizer Recharge retention of about 80% of its runtime after 105 cycles really better than the Sanyo Eneloop retention of 60% of its runtime after 314 cycles? Directly comparing their end-of-life performance is crazy; the Eneloop got three times as many cycles!

What would have happened to the Eneloop's runtime after just 105 cycles? As it turns out, not a lot. Accelerated test data from Sanyo (something more battery makers should be unafraid to publish!) shows Eneloops are still going strong with roughly full capacity up to about 200 cycles, a point when all of the other batteries in the Consumer test were already dead or well on their way out.

The capacity of Eneloops also actually improves a little in their first few cycles. (My own testing – see "Update 20 June 2007" under the AA detailed notes – shows that after half a year of use they get up to 2116 mAh.) The capacity of ordinary (non-LSD) NiMH batteries starts decreasing right from their first cycle. The Energizer Recharge would have started deteriorating quickly after just 50 cycles, and had less capacity than the Eneloop after only about 60 or 70 cycles. How can Consumer consider that a more consistent battery?

This graph is not from the Consumer test data (which they did not publish with their report). It is based on Sanyo's fast cycle test data, and is supported by fast charge data from SilverFox and others on CandlePowerForums. Remember, Consumer thought these two batteries rated only 1% different from each other in their final scores, and because of the serious doubt that a 0.9 V termination voltage was used it's likely that the Energizer Recharge would actually have achieved significantly fewer cycles than Consumer says it did.

From the graph, since the capacity of the Sanyo Eneloop is basically unchanged at 105 cycles (the life of the Energizer) it's reasonable to assume that the Eneloop's runtime will also not be significantly decreased at that point. 80% of the Energizer Recharge's original runtime would come in at less than the Sanyo Eneloop runtime by the time the Eneloop had done 105 cycles, even without considering the very undesirable loss of voltage causing the Energizers to be crappy batteries by that stage. If Consumer was running a fair test then the Eneloop – and probably most of the good LSD batteries – would have rated at or near 100% for consistency at 105 cycles.

The basic point that can be seen from this is that if the Eneloop batteries had just been thrown out after only a third of their cycles they would have rated higher, while still completing the same number of cycles as the Energizers. That's absolutely crazy!

This is another serious failing of the Consumer test.

Let's see how this changes things at the point the Energizer Recharge got to.

Battery Consistency/
Crappiness
Original
Overall Score
Corrected
Consistency
@ 105 cycles
Corrected
Overall Score
@ 105 cycles
Energizer Recharge 8.0 69 6.3 64
Sanyo Eneloop 6.0 70 10.0 82

The simple truth is that having a little bit extra runtime based on a battery's capacity when new is of no real value if the battery quickly become unreliable. If extra runtime when batteries are old is directly due to a sagging voltage under load it's very dodgy to claim that extra runtime is good.

Cost

Consumer paid lip service to cost by listing the prices of single batteries, but there's strangely no indication whether this contributed to the final score for each battery, and no attempt was made to compare the cost effectiveness of the batteries over their life. Not surprisingly Consumer did not consider the cost of frustration with crappy batteries either, or how bad batteries would just be left in a drawer (which doesn't give a good return on investment).

There's also a problem with the price Consumer listed for a 4 pack of AA Sanyo Eneloops. They are commonly available nationwide with free delivery for $24.99 from Dick Smith Electronics [broken link; update Jan 2016 they're now in receivership], or just $22.89 [broken link] from PB Tech (update: $20.59 in Jan 2013; update: $16.04 for 3rd generation Eneloops in Sep 2013) – significantly less than the $28 Consumer mentions. (If you don't mind waiting for international shipping they're also available for about $21 here [sold out], or about $19 here [sold out], shipping included for both.) Price comparison web sites PriceSpy and PriceMe don't list any for $28, so where did Consumer get them from? Evidently not a major chain.

Unless... Consumer has used Dick Smith Electronics' 2xAA price of $13.99 and doubled it. (It's possible that's all they got and just used one of them for cycle testing and the other for the self discharge test, but in the article they included a photo of a 4 pack. Misleading? Cheap?)

Battery Cost per Battery Cycles Cents per Cycle
Sanyo Eneloop

$5.72 or $6.25
(not $7.00)

Jan 2013: $5.15
Sep 2013: $4.01

314

1.8 or 2.0

Jan 2013: 1.6
Sep 2013:
1.3*

Duracell Active Charge $5.25 196 2.7
Energizer Recharge $7.00 104 6.7
Vapex $5.75 53 10.8

*Assuming no increase in cycles from 3rd generation Eneloops.

The Energizer Recharge cost 3.7 times as much per cycle as the Sanyo Eneloop (and remember the graph in the Runtime and Cycle Life section above showed the Eneloop had a higher average capacity).

These Cents per Cycle figures do not include the cost of electricity required to charge these batteries, which is almost negligible. At just 23.5 c/kWh (NZ$) it costs less than 0.1 cents to charge even the highest capacity battery, while still allowing for charging inefficiency of the battery and the power the charger itself uses. The Duracell Active Charge (a LSD battery) had the second lowest cost per cycle. The Vapex was one of the cheapest batteries in the test but the most expensive per cycle. Paying extra is no guarantee of quality.

The Sanyo Eneloop offers the best value for money; it's sad that Consumer couldn't bother to highlight how much better they are for value.

This is yet another failing of the Consumer test.

Self Discharge

Self discharge is the tendency of NiMH batteries (and other sorts of batteries as well) to go flat while sitting around doing nothing, whether on a shelf, down the back of a sofa, or in a digital camera hidden away in a drawer. It's a problem because when they're needed, a battery can be completely flat because of self discharge (assuming the camera doesn't have a small parasitic discharge, which would flatten it more quickly). Particularly bad batteries can lose most of their charge overnight, meaning they always have to be charged immediately before use. It's like a car with a hole in the bottom of its fuel tank.

Low self discharge batteries – unfortunately abbreviating to LSD – were invented to address the problem, with the first being the Sanyo Eneloop. At last there was a NiMH battery that didn't need to be charged immediately prior to every use!

Their LSD ability worked so well the Eneloop revolutionised the rechargeable battery market. The concept has been so popular that all battery makers – with the notable exception of Energizer – now have LSD batteries amongst their products. LSD batteries are normally sold as "ready to use" or "pre-charged" because thanks to their LSD ability they can be sold with a partial charge. Normal NiMH batteries are completely flat when bought.

In the comments for the report on the Consumer web site, doubt has been raised about the validity of the self discharge test results. Many battery users are familiar with how quickly non-LSD batteries self discharge, and the 12 week duration of the self discharge test should have been long enough to clearly show the benefit of LSD batteries – test data shows non-LSD batteries typically have roughly twice the self discharge at 3 months that LSD batteries have. Consumer's results did not show that. Why not?

The self discharge figures in the Consumer article were no doubt measured when the batteries were brand new. While it's interesting to know, this is next to useless information as the self discharge characteristics of non-LSD NiMH batteries can change significantly after even a small amount of use. The self discharge of brand new non-LSD batteries is not characteristic of how they will perform later in their life. The test thus favours the non-LSD batteries. Give them a couple of dozen cycles and then see how well they do for self discharge! This would be a far more realistic test and give far more useful information. The voltage under load should also be measured as it is lower the longer a battery has been sitting idle.

The self discharge test was only 12 weeks long. Longer term testing has shown that brand new fully charged NiMH batteries will still have usable capacity after 3 months (13 weeks), perhaps losing 20-25%. However, after six months it would be very unexpected if any new non-LSD batteries had any capacity left at all – their self discharge rapidly increases after 3 months. Conversely the best LSD batteries would probably not have lost much more capacity – their self discharge slows down after 3 months. Thus, using a comparatively short self discharge test also favours the non-LSD batteries.

It seems disingenuous of Consumer to have tested new batteries after only 12 weeks when any good researcher looking into self discharge should have unearthed this information and been able to devise a fairer, more representative test.

It's also possible that battery manufacturers are just gradually incorporating some of the LSD manufacturing methods in their non-LSD batteries, leading to more robust batteries that (at least when new) self discharge at a slower rate.

A very revealing 2007 test looked at self discharge of used Panasonic, Duracell and Energizer NiMH batteries. In just one week, 4 of the 6 Energizer batteries were almost completely flat because of self discharge, and no practical use for photo flashes.

We took several samples of each battery that had been used for 3 years in the same conditions and the same number of uses. Also, they have received the same amount of care and maintenance, recharging and usage.

...

As can be seen in figure 1, while cell #6 discharged slowly over a period of 100's of hours, the rest of the batteries discharged quite rapidly, becoming useless within 4 days. These results confirmed what we suspected - there is something wrong with several of our cells.

Many people think the capacity of a rechargeable battery is the most important characteristic. It's a single number that's easy to understand and allows batteries to be easily compared. Unfortunately the claimed capacity is seldom the actual capacity, especially with non-LSD batteries after they have been used for several cycles. The capacity also makes no consideration of voltage under load, which affects the power the battery can supply; nor does it indicate how reliably the battery will maintain its charge if left for several days or what voltage it will be able to supply under load after an extended storage time.

Whether battery users realise it or not, low self discharge is far more desirable to the average user than high capacity. This is because most people want a reliable battery that will have a good charge when they come to use it. They don't want to worry about high self discharge and unreliable batteries, or having to plan when to charge batteries so they'll be ready just before they're needed. This is one of the main reasons that people don't use rechargeable batteries and why they tend to just sit in a drawer doing nothing.

Low self discharge batteries are what most users should be buying.

Batteries for an Emergency Pack

Alkaline batteries were recommended by Consumer as "still best for an emergency pack because they lose very little charge when stored for extended periods." It was a strange recommendation because the test was exclusively for rechargeable NiMH batteries; no test data or other supporting evidence was included or even referred to in support of any use of alkaline batteries, and no test data was included regarding LSD batteries after extended storage. Their recommendation was completely unsupported by evidence.

The truth is that alkaline batteries may hold their charge, or they may be unusable after a relatively short period of storage. Alkaline batteries can go flat or even leak in storage, and exposure to heat is particularly bad for contributing to this. Alkalines should be stored in a cool location. Even without heat, the voltage that alkalines can provide under load slowly deteriorates, so alkalines stored for long periods may be rejected by high drain devices (even if they weren't already rejected brand new).

Alkaline batteries do not cope well with moderate to heavy loads, and do not compare well with good NiMH batteries in those situations. Read Roy Lewallen's excellent "1.2 Volt" vs. "1.5 Volt" Batteries PDF for further information.

Quite apart from the question of whether the batteries will be able to do what you want when you eventually need them, the capacity (and stored energy) of alkaline batteries declines over time, so putting alkaline batteries in an emergency kit is basically evaporating your money.

It's a shame Consumer didn't bother assessing how good LSD batteries might actually be in an emergency pack. Some LSD batteries presently on sale are rated for 70% charge after 3 years – easily enough capacity to provide a useable amount of runtime. Consumer only looked at self discharge after 12 weeks. Consumer's claim they are not suitable is not based on their own testing and is an argument from silence.

This is yet another failing of the Consumer test.

Besides having a good shelf life, LSD batteries are of course fully rechargeable at any stage, and usable for any temporary task at any time without worrying about having to buy a new set of batteries to replace them with in the emergency pack. This is a significant improvement in convenience. Rechargeable batteries only have to be used a handful of times before they're more cost effective than alkalines – less than 3 times for the top brands of alkalines.

LSD batteries are now a real option for emergency pack batteries.

FWIW the next (third) version of Eneloop was announced earlier this month (October 2011). They will retain 90% charge after 1 year and 70% charge after 5 years, and claim 1800 (slow) recharges. Initially they'll be sold only in Japan, starting on 14 November 2011.

Update Sep 2013: These are now being sold at PB Technologies.

Update Sep 2016: The generation of Eneloop presently sold by PB Tech claims 65% capacity retention after 5 years and to deliver up to 2100 (slow) recharges, but the latest generation of Eneloop claims 70% capacity remains after 10 years, with up to 2100 charges.

Update October 2017: Consumer was completely wrong about Eneloops being unsuitable for emergency packs. That's not too surprising, since they reached their conclusion completely without (and even ignoring) evidence or adequate research into the low self discharge ability of Eneloops. I've just tested some "brand new" 3rd generation Eneloops which were actually manufactured over four years ago and just sitting in a box (or on a shelf) since then, unopened. When Eneloops are made they're given a ¾ charge, and because they only slowly discharge, they still have a pretty good charge when they're bought and used for the first time. These ones still had 83% of their inital ¾ charge. The evidence is clear: Eneloops are great for emergency packs.

Other Problems With the Test

  • In the side box explanation for milliamp-hours, the phrase "milliamps per hour" in the last line is meaningless or stupid. Or both. Take your pick.

  • The Endurance figure, worth a huge 60% of the total, is a complete mystery. It allegedly "assesses battery life including running-time per charge and the number of charge/discharge cycles." And some magic, by the looks of it. The Kodak figures for both Endurance and Running-Time are about 8% higher than those for the Sanyo Eneloop, but the Cycles Completed figure for the Eneloop is 45% higher than that of the Kodak. If the two had completed the same number of cycles then it would be easier to guess that the cycles figure had just been completely ignored to get from an 8% higher Running-Time to an 8% higher Endurance for the Kodak. How was the Endurance figure calculated?

    Battery Initial Capacity Initial Runtime Cycles Endurance
    Kodak Digital Camera Battery

    2179 mAh

    5.3% higher

    120 minutes

    8.1% higher

    216

    7.8

    8.3% higher

    Sanyo Eneloop 2068 mAh 111 minutes

    314

    45% higher

    7.2
  • The Eneloop and the Eveready got the same total score, 70%. Together they provide another example of how the Endurance figures must have involved some magic and completely ignored the Cycles. Compared with the Eveready, the Eneloop's capacity was 2.9% higher, its initial runtime 1.8% higher, its cycles 44% higher. But Consumer gave the Eneloop an Endurance score just 1.4% higher. (The only way the Eveready scored higher than the Eneloop was its Crappiness score, 6.3 vs 6.0.) Clearly the much higher cycles the Eneloop achieved don't count for anything, yet very low cycles do appear to have counted against some of the non-LSD batteries.

    Battery Initial Capacity Initial Runtime Cycles Endurance
    Sanyo Eneloop

    2068 mAh

    2.9% higher

    111 minutes

    1.8% higher

    314

    44% higher

    7.2

    1.4% higher

    Eveready

    2010 mAh

    109 minutes

    218

    7.1
  • The Endurance value's reliance on "running-time per charge" is quite ridiculous, because the running time in a fixed resistance test (as shown in Faulty Understanding of How Batteries Work above) is directly dependent on the voltage. The lower the voltage, the lower the current, which means the performance is worse but the runtime is longer. It's probable that Consumer has stuffed up this value as well as their Crappiness score, giving high scores to batteries which maintained high runtimes instead of high voltage. This means that the Consumer test has almost no value at all.

  • A new Eneloop will manage an average 1.25 V quite comfortably at 1 A constant current discharge. From the initial current figure calculated for it above (1.12 A) this would imply a resistor of about 1.1 Ω could have been used to discharge the batteries. But the initial average current figure of 1.23 A for the Powertech battery rules that out since a 1.1 Ω resistor would mean an average voltage of 1.35 V during the first discharge. Not even Eneloops can do that. So if a constant resistance was used in the test then a 1 Ω resistor was the most likely used. Eneloops have been widely tested to hold their voltage very well under load (even up to an amazing 10 A) so why was the initial average discharge current for the Eneloop only 1.12 A? It seems that Consumer's testing was simply quite inconsistent.

  • Taking a look at all the average initial currents, the Powertech's 1.23 A is anomalously high. It's firmly an unexplained outlier and is an indication Consumer's testing was inconsistent.

  • A probable test load of a 1 Ω resistor means the Energizer Recharge battery would have maintained an average (!) voltage of only 0.68 V during a discharge at the end of its life. Battery discharges are normally terminated at 0.9 V (or sometimes 0.8 V). With a healthy NiMH battery which maintains a good voltage under load there's no reason to discharge any lower because there's no more capacity to be gained and damage to the battery to be risked by a deep discharge. Devices designed for a typical 1.2V will likely not be remotely happy with just 0.68 V. At what voltage (or by what other condition) were the discharges terminated?

  • A fixed resistance test will penalise good batteries for runtime, since it will draw more current from batteries that can hold a high voltage under load, making them discharge sooner. A good test would use either a constant current discharge (like the Maha MH-C9000 uses) or use a fixed resistance but measure the battery's voltage as it discharges so the battery's energy in mWh can be calculated (like I used for my Li-ion battery tests).

    Power = Current * Voltage
    Capacity = Current * Time
    Energy = Capacity * Voltage

  • A fixed resistance load will tend to even out any voltage difference. When the battery voltage is high (at the start of the whole test or each discharge) a high current will be drawn, causing more voltage drop. When the voltage is low (at the end of the test or each discharge) a smaller current will be drawn, causing less voltage drop. This effect will not be huge for good NiMH batteries, but it may be significant for poor quality batteries with high internal resistance. For the average current to have changed so much for some of the batteries emphasises just how bad a state the batteries must have been in at the end of the test and makes me ask again: At what voltage (or by what other condition) were the discharges terminated?

Other Notes

  • The Kodak batteries were labeled Digital Camera Batteries and it's not surprising to see that they got the equal lowest Consumer Crappiness score, meaning they held their voltage in the Consumer test quite well over their life. A good voltage under load is important for digital cameras, which is one big reason why alkalines do not perform well in them. Batteries with high Crappiness scores will also not perform well in digital cameras in the long term.

Conclusions

  • Most battery buyers should get LSD batteries.

  • High capacity batteries have a short usable life (managing few cycles before becoming useless in the real world) and are likely to become unreliable after just a few dozen cycles. (One exception is the Eneloop XX, aka Eneloop Pro, although there is still a trade-off for cycles and LSD compared to standard Eneloop batteries.) High capacity batteries have their uses, but are not well suited to the average user. Capacity at the expense of reliability is not normally a good thing.

  • The Sanyo Eneloop has by far the longest cycle life of commonly available batteries and is the least expensive per cycle.

  • Good quality LSD batteries (especially the 3rd generation Eneloop) may be the best option for emergency pack batteries. They are the most convenient, most cost effective, least likely to leak, can be topped up at any stage, and perform well under heavy loads. Alkalines are not a good choice because they permanently lose capacity in storage so may be of little use when eventually needed, and they may also leak in storage, including in an expensive device.

  • Consumer has failed to run a fair or accurate battery test. This is particularly evident in their Crappiness score which clearly penalised the actually well-performing LSD batteries, and that the Eneloops would have scored better if they had been discarded after just a third of their life – around the same cycles as the Energizers achieved. Consumer's Endurance score also looks screwed up. With those values at 30% and 60% of the total score respectively, there's not a lot that's not screwed up with this test. (The remaining 10% is a Self Discharge value.)

Responses from readers

  • "Consumer is in la-la land if they think there's only 1% difference between Eneloops and Energizers."

  • "They're misrepresenting Sanyo's product. They've misrepresented them so badly it's verging on libelous. Are they going to publish a correction?"

Updates

  • 22 October 2011: I sent an email to Consumer report writer Paul Smith with some of my concerns. Neither he nor Consumer has responded (other than their auto-reply). Well, what could they say? "Yes, we badly stuffed up the test and the analysis but we believe the report is still of value to our customers"? Acknowledge the report isn't worth the paper it was printed on? Yeah, right. Fat chance of them admitting that, since almost every part of the test had something wrong with it. Better to just keep quiet.

  • November 2011: The November Consumer magazine has a paragraph about report writer Paul Smith. "His passion is product quality and he abhors badly designed products." I have to ask – why doesn't Paul Smith abhor badly designed tests that can't identify quality products?

  • 27 November 2011: A simple battery test of some crap Energizer batteries supports what I was saying above – the claim of 105 cycles for the Energizer Recharge 2450mAh battery is ridiculous because with its high Crappiness value it would be useless for many important tasks long before it got to that many cycles.

Yesterday I was handed a pair of Energizer 2500mAh batteries to charge because they had been rejected by their normal charger. It turned out they were almost fully charged, and yet they had also been rejected by a digital camera; hence why their owner wanted to charge them.

The Energizer 2500mAh has a very bad reputation for being a crap NiMH battery so I offered to give them a full cycle on my Maha MH-C9000 battery analyser to see how much capacity they now have.

The MH-C9000 test cycle showed they have 83% of the claimed 2500mAh capacity, with quite a low mid-point voltage. The Consumer test last month ran batteries until they had only 50% of their capacity left, but even with 83% of their supposed original capacity these Energizer batteries still couldn't power a digital camera when nearly fully charged.

  • 19 January 2013: Several updates including an Eneloop price drop from PB Technologies – see above in the Cost section for the link. Also a link added to a self discharge test on used batteries – see the Self Discharge test section.

  • 1 September 2013: Minor updates like taking out a non-working link and adding references to 3rd generation Eneloops, now available from PB Technologies.

  • 10 August 2015: Minor wordng updates and took out a non-working link.

  • 7 January 2016: Dick Smith now in receivership. Not a good source for batteries.

  • 11 September 2016: Improved the wording in a few places above. Battery news of the moment:

    • Dick Smith had enough stock of alkaline AA batteries to last 12 years, and enough AAA batteries to last 11 years.
    • Consumer magazine has published a new battery test. Surprise! It's not completely abysmal like their 2011 one was. Indeed, the report goes to some lengths to explain exactly what they've done (and thus how they haven't made some of the shockingly bad mistakes of the previous test). But they still don't recommend Eneloops for emergency packs.
  • 2 October 2017: Minor wording changes and added a test result showing very clearly that Eneloops are excellent for emergency packs.

    For non-rechargeable batteries Consumer magazine still hasn't learned. On their disposable batteries testing page:

    How we test

    Each AA battery goes through high- and low-drain tests to assess how they perform in different gadgets – we averaged the results from four examples of each model in every test. We measure how long they last in each test and the amount of energy they deliver over that time, then convert these measurements into a performance score. The low-drain test uses a load of 24 Ohms, while the high-drain test uses a 2 Ohm-load [sic].

    Our performance scores are weighted evenly between performance and run time from each battery’s starting voltage of 1.5V down to 1.0V then to 0.7V – some devices start to falter and won’t operate at 1.0V; we use 0.7V as our benchmark for completely empty. We also calculate a ‘Value’ score based on how much each hour of use costs.

    First, ohm is a unit and doesn't get a capital letter except at the start of a sentence.

    Next, testing with fixed resistance is nice and simple – I've used it myself to test Li-ion cells – but as previously explained, high resistance batteries have a lower voltage under load. This means they can supply less current through a fixed resistance (Ohm's Law, V=IR), so take longer to discharge, so get longer runtime, so incorrectly achieve a better Consumer value score. With my Li-ion tests I make voltage/capacity and voltage/energy graphs, so a much much better idea of actual performance can be obtained.

    Also as previously mentioned, alkaline batteries do not cope well with moderate to heavy loads. The amount of energy an alkaline battery can deliver changes greatly depending on how quickly it's used. The lower the load on an alkaline, the more energy it can deliver. Decrease the current and the battery's total energy delivered – and thus runtime – increases. The effect is much smaller for NiMH batteries, but can be quite significant for alkaline batteries. Adding a resistor in series with an alkaline cell will show it, so the extra 22 Ω in the 24 Ω test will result in significantly greater energy figures and runtime than the 2 Ω test. Internal resistance will also do this to some degree, and again contributes (hopefully only in a small way) to longer runtime and an incorrectly higher value score.

    It's about time Consumer reconsidered how they test batteries. A simple treatment of using the runtime to calculate value like Consumer has means bad batteries with high internal resistance are falsely favoured.

    In their online rechargeable batteries report Consumer mentions a very strange unit: kilogram-seconds. This is another secondary school science fail for Consumer. The symbol for kilograms is just kg. Units do not get pluralised.

    Also, it would be interesting to know if the ruggedness test was just physical (as it seems) or if the batteries were capacity tested after the test. Some brands of high capacity batteries are regarded as being quite delicate and with each knock would probably have lost capacity or their ability to hold voltage under load. Even Eneloops are not immune to rough treatment.



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