So far we have been testing and reporting the Amp-Hours (Ah) of the various batteries we have tested with the reason being that they are usually being rated in Ah regarding their capacity. But there is another unit that may actually give a better idea about the capacity of a battery and it is Watt-hours (Wh) when talking about batteries. This is precisely the reason why we have decided to also include not only the measured Ah in our battery tests, but also the Wh values – the good thing is that we actually should have all of these for the batteries we’ve tested so far and we are going to include the Wh results for all tests already done.

With each battery we usually have two important ratings, though both are usually revealed by the manufacturer only for rechargeable batteries – Voltage and Amp-Hours (usually written in mAh). Different batteries may have different voltages and capacities and normally you should do some math to know what you can expect from a battery if you know the power requirements of the device you need the battery for. Here is an example: an AA type of NiMH rechargeable battery that has a typical voltage of 1.2V and is rated at 2000 mAh (2 Ah) should be able to power a device requiring 2 Amps for 1 hour, or a device requiring 1 Amp for 2 hours and so on. However when measuring the actual battery performance life in our tests you can clearly see that the starting voltage of a fully charger NiMH battery is higher than the official 1.2V rating and when the battery is considered discharged it is lets say at 1V. So by switching from the Ah to Wh we can take into account the changing voltage of the battery while it is being discharged and get even better idea about its actual energy capacity, even though the Amp-Hours ratings usually do a good job for comparing batteries.

To get an estimate about the Watt-Hours rating of a battery you need to multiply the Amp-Hours by the Volt rating of the battery. So for the above example with 1.2V NiMH battery with 2 Ah capacity we are going to get 2.4 Wh, meaning that this battery can power a device with power consumption of 2.4 Watts for 1 hour, or for 2 hours if it uses 1.2 Watts and so on. But this is just an estimate, because as we’ve already said the voltage of the battery will vary while it is being discharged, so we need to do a thorough test measuring the full discharge cycle to get more accurate value. If you look at the discharge graph and the Amp-Hours in our battery tests with different loads you will see how the voltage is different at different load levels and this will also affect the Watt-Hour ratings as well.

Another thing that we are going to be adding soon are tables that will make it easier for you to compare the performance of all of the batteries that we have tested, of course the tabled results will be divided by battery type. This should allow you to quickly get an idea what could be the best choice for your particular needs for a battery…

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• Carbon-Zinc, Alkaline, NiMH, LSD NiMH… What Battery to Use and When to Use it
• Ampere-Hours or Watt-Hours is Better for Batteries
• Be Careful With the Expiration Dates of Primary Batteries