Batteries

An Objective Comparison of Major Battery Varieties

Introduction

People lie. People selling lie more. So it’s no surprise that manufacturer stated battery capacities are not entirely accurate. In reality most manufacturers don’t outright lie, but they do change the rules and move the goal posts a bit so that their batteries appear in the best possible light.

This page contains some information from testing and comparing various batteries. Rather than using misleading industry self-selected conventions, all batteries are compared on a equal basis to give a clear and representative picture of how batteries rate against each other.

My focus for batteries is outdoor use in high load situations such as high intensity lights and in lower load situations like GPSs and radios. I have a particular interest in fast-and-light back country travel and in search and rescue. In the latter case, rapid deployment and dependability are essential. The stringent requirements for my interests mean that the same information should apply well to a broad range of more general applications use such as cameras, MP3 players, etc.

This page is a work in progress and will be continually updated with more information as further tests are completed. I’m only just beginning… If you have any batteries you would like added to this page, please let me know.

Conclusion

I thought it might be best to just start off with the conclusions. I realise it’s not the way things are normally done, but for most people the detail of this page is too much information. So here’s the conclusions and summary.

Battery Type Conclusions

It would be a good idea to quickly talk about the various battery types here, because there are a few non-obvious facts about what you should and shouldn’t use them for, and pros and cons with each type. Some of this information comes from the results of the tests and some is more general knowledge.

Primary cell

The primary cell is a chemical battery for single use only and can not be recharged.

Pros:

  • Fairly cheap for one-off use
  • Can be stored for extended periods without degrading. This makes them the sensible choice for low maintenance batteries. These are the ones you want in your emergency kit. It also makes them the sensible choice for smoke detectors, clocks, and other things you want to last for a long time.
  • Slightly higher voltage that NiCd and NiMh batteries. This means torches and headlights will shine more brightly with primary cell batteries. But remember that this is a very short lived effect, so don’t be swayed too much by it.

Cons:

  • Become expensive if replaced often
  • Have relatively low capacities in high drain applications and for many real-world situations.

NiCd (Nickel Cadmium)

Pros:

  • Works with a simple charger (not damaged by trickle charging)
  • Can supply extremely high power levels for short periods. This is useful in things like power tools, cars, explosives detonators and the like. For general applications this sort of extreme current is not required.

Cons:

  • Rapidly loses its charge (approximately 30% per month). This means you can’t really keep these batteries charged on standby for rapid deployment, without taking special measures. They are also not much use in anything you want to last for a long time like smoke detectors and clocks.
  • Compare poorly to NiMh for capacity. With NiMh chargers now readily available, there is very little reason to want to buy NiCd batteries.

NiMh (Nicket Metal Hydride)

Pros:

  • These are the highest capacity consumer-ready batteries. For rechargeables, these are the ones to buy.

Cons:

  • Rapidly loses its charge (approximately 30% per month). This means you can’t really keep these batteries charged on standby for rapid deployment, without taking special measures. They are also not much use in anything you want to last for a long time like smoke detectors and clocks.
  • Requires a special “smart” charger to charge, otherwise batteries are likely to be damaged. Not all smart chargers are created equal, and many are complete rubbish.

Li-Ion (Lithium Ion)

Pros:

  • Highest capacity of batteries
  • Technically simpler to charge the NiMh batteries

Cons:

  • Chargers are not readily available (yet), so practically speaking, they are hard to charge.

The Best Battery

[Coming soon]

Batteries; Head to Head

Here’s the results. By way of comparison, a peanut (dry roasted) contains about 25000J of energy. That puts our current battery technology into perspective 🙂

Battery Rated capacity Measured capacity Effective capacity
Energizer Ultimate Lithium L91 AA (Primary cell) 3000mAh (0.25A) 16685J (4.63Wh) 3862mAh
Eveready Lithium AA (Primary cell) 14757J (4.10Wh) 3416mAh
Energizer Recharge AA (NiMh) 2450mAh 11656J (3.24Wh) 2698mAh
DSE NiMh AA (NiMh) 2500mAh 9457J (2.63Wh) 2189mAh
Energizer Advanced X91 AA(Primary cell) 2050mAh (0.25A) 8533J (2.37Wh) 1975mAh
Maxuss 3000 AA (NiMh) 3000mAh 7938J (2.21Wh) 1837mAh
Energizer Max E91 AA (Primary cell) 1900mAh (0.25A) 7895J (2.19Wh) 1827mAh
Eveready Gold A91 AA (Primary cell) 7319J (2.03Wh) 1694mAh
Energizer Ultimate Lithium L92 AAA (Primary cell) 1200mAh (0.2A)
Energizer Recharge AAA (NiMh) 900mAh 3934J (1.09Wh) 910mAh
BTY 1350 AAA (NiMh) 1350mAh 3930J (1.09Wh) 910mAh
Energizer Advanced X92 AAA (Primary cell) 750mAh (0.2A) 3549J (0.99Wh) 821mAh
Energizer Max E92 AAA (Primary cell) 700mAh (0.2A)
Eveready Super Heavy Duty AA (Primary cell) 3059J (0.85Wh) 708mAh
Eveready Gold A92 AAA (Primary cell) 2739J (0.76Wh) 634mAh
Eveready Super Heavy Duty AAA (Primary cell) 986J (0.27Wh) 228mAh

More batteries on the way…

Cost Effectiveness

[Coming soon]

Warning: what follows is a slightly more technical discussion of the methodology and findings. The conclusion above contains most of the useful top level details.

The Gory Details

Capacity in High Loads

The industry “standard” for measuring battery capacity is to drain a battery at such a rate that it is depleted in 10 hours. The current and voltage are measured to determine the overall energy capacity of the battery. The normal convention is to state the capacity in milliampere-hours (mAh). However given that the voltage changes over time, this is a very poor indicator of energy capacity. The normal scientific measure of energy is the joule, which is what I list capacities in. The watt-hour (Wh) measures the same thing and is a common unit for electrical capacities so I also state that.

The 10-hour test is a terrible test since an inferior battery is tested at a lower load and will appear to perform better than it should. This is one of the tricks manufacturers depend on to make their batteries look good. Instead, the test I use drives all batteries at the same load. The load is selected by choosing a nominal and “perfect” 2500mAh 1.2V battery as the point of comparison. To deplete such a battery in 10 hours would require a load of 2500mAh / 10h = 250mA. At a voltage of 1.2V, assuming negligible internal resistance, then by Ohms law, R=V/I = 1.2V / 0.25A = 4.8Ω to achieve this load.

Here is a chart showing battery voltage over time for the various batteries.


It is important to note that the overall energy capacity is effectively the area beneath the line. So for primary cell batteries, which continually degrade in voltage over time, the area beneath the curve is relatively small compared to the NiMh curves, even though the battery might last a similar time overall. In the case of an LED headlight, for example, the effect of this is that a primary cell battery would be quite dim compared to the NiMh battery. They might both last 10 hours, but you’d get more light out of the NiMh battery overall. The primary cell batteries actually have a slightly higher voltage when they’re fresh. The effect of that would be a brighter light initially. This is a claim you often hear to suggest primary cells are better for lights, but of course as you can see from the chart the effect is very short lived and it’s not long before the power output drops well below the NiMh batteries.

Capacity in High Non-linear Loads

[Coming soon]

Capacity in Low Loads

[Coming soonish]

Capacity in Repetitive Loads

[Coming soonishish]

Longevity/Memory

[Coming later]

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