Research Topic: Which Battery Will Do?
Question: What type of battery should I use? Zinc-carbon, alkaline, lithium or rechargeable? What form of battery should I use? Button cell, car battery or something in between?
Note: Often the words are used interchangeably, but a battery is technically a series of cells. For example, a 9V battery really is a battery (made of six 1.5V cells) but an AA battery is a single cell.
Answer: In a nutshell, for general use for almost any AA or AAA task I recommend the Sanyo Eneloop, a low self discharge rechargeable NiMH cell, combined with a good charger.
Low self discharge cells go flat very slowly, and Eneloops extremely slowly, so Eneloops are still charged even after months (or years!) of sitting around doing nothing. While Sanyo Eneloops are now the only AA or AAA batteries I buy, other reputable brands of low self discharge cells have been tested to give almost as good performance, but not for as many cycles.
High capacity rechargeable cells (eg, 2450 mAh, 2500 mAh or more) have more capacity initially but last far fewer charge cycles and can quickly deteriorate so they self discharge very rapidly, going completely flat in days. They are a recipe for frustration, and I recommend consumers stay well clear of them. The exception is the Sanyo XX 2500mAh NiMH cell which uses technology from the low self discharge Eneloop. It sacrifices extreme shelf life and cycle life for a higher capacity than normal Eneloops.
As a convenient replacement for D cells I recommend the use of AA to D converter cases that each take two AA cells in parallel (although note that some torch springs have trouble with the size of the negative contact). These converters mean D cell torches can easily be run on AA cells, meaning that a special charger for D cells doesn't need to be bought - your normal AA charger will do the job.
If non-rechargeable, single use cells are still wanted for some reason, I recommend inexpensive generic brand alkaline cells. While the top brands normally perform a little better than generic brands they don't give good value for money, especially compared with rechargeable cells like Eneloops.
Heavy duty and super heavy duty batteries are pathetic in all situations. I honestly don't know why it's still legal to sell them, especially considering some of the marketing claims made for them.
If the form of battery is predetermined (for example, if you want D cells for a torch, an AA cell for a clock, etc) then that makes the choice much simpler. If designing a battery-using project from the ground up (where you need to choose the form of battery) take a perusal through the tables on the following pages.
To answer the first question, numerous tests come to the same conclusion - since batteries are basically a commodity they are most economically purchased according to price. More expensive batteries will last longer but will very likely be less cost effective. So if cost is an important consideration and it doesn't matter how often you change the batteries (or how much landfill you produce) just buy the cheapest battery you can find - normally a zinc-carbon (normally sold as "super heavy duty") or a cheap alkaline.
For those uses that require long shelf life or higher power demands (longer time, greater current etc), go for alkaline batteries. In battery tests available on the web Duracell is widely regarded as the best commonly available brand, lasting the longest although often with a price to match. However, here in New Zealand I've seen 10 Duracell AA batteries for the same price as 8 Energizer AAs (another reputable brand).
For high current applications (like digital cameras) that are not used very often use "next generation" alkalines like Duracell Ultra or a new alkaline type, nickel oxyhydroxide (NiOOH), such as Panasonic's Oxyride, sold specifically for digital cameras. Another new option is low self discharge rechargeable cells, like Sanyo's Eneloop.
If you need AA cells and both weight and life (at medium to high current) are extremely important and price isn't an issue then lithium/iron disulfide is the way to go. Energizer's patent has expired, so there are some slightly cheaper versions to be found.
If you need high current, really high current, or good life at high current try rechargeables. They also work out very economically in the long term, and can outlast alkalines at medium and high current. (Good alkalines still outlast most rechargeables at low current.) This makes rechargeables ideal for digital cameras that are used often. Low self discharge cells like the Sanyo Eneloop are a very good replacement for AA and AAA batteries in a wide range of devices. See the Recommended Batteries for Particular Uses page for examples.
There are many different battery types and all have advantages and disadvantages, but they all hold some things in common. For example, the often repeated advice to not mix battery types or mix old and new batteries is because if one cell discharges before the others it may get reverse charged by the still-good cells. That may cause it to leak or even explode.
Often the words are used interchangeably, but a battery is technically a series of cells. For example, a 9V battery really is a battery (made of six 1.5V cells) but an AA battery is a single cell.
As well as the physical dimensions and weight of a battery, it can also be measured in several other ways:
One way of measuring a battery is by its storage density. For example, an alkaline AA battery can provide more power than a zinc-carbon for the same size and so is said to have a greater storage density. Storage density can be based on weight (gravimetric storage density, or specific energy, in Wh/kg) or volume (volumetric storage density, or energy density, in Wh/L).
For example, a Duracell Ultra AA (MN1500) has a specific energy of 143 watt-hours per kilogram (143 Wh/kg) or an energy density of 428 watt-hours per litre (428 Wh/L). The actual (nominal) capacity is 2.85Ah, but that's with a load of 43 ohms (an initial current of 35mA) and for higher currents the battery has a much lower capacity - the Peukert Effect. At 1 amp current it only has 0.781Ah according to Dave Etchells' test.
Rechargeable batteries however do much better at high current, and recent high capacity cells can manage as much as 2.57Ah (or even 2.7Ah hot off the charger) at 1 amp drain.
Conversion efficiency is how much of a battery's energy is output as electricity, rather than generating heat, etc. Batteries with a low internal resistance will have a high conversion efficiency (and be able to output high currents).
Read on for information about single-use battery types.