We are! We have decided to try to find out how much energy there actually is in your average battery. There are so many brands, names, categories and types it is very unclear what you actually get for your money. Should you buy an expensive alkaline battery or would a cheaper brand suffice. Batteries use descriptive words like, superpower, power plus or extra energy to describe what you get, but there is no data on the side of batteries to quantify what you are buying. So we have decided to find out.
There are complications in calculating the energy in a battery, since the energy of the output varies with the change in voltage as a battery is discharged at a given rate (mAh specified). An absolute number for the capacity of the battery (the number of mAh) can however be evaluated easily by setting the discharge current of the test apparatus to a fixed value. If you are then willing to accept an approximation of energy by averaging the discharge voltage over the discharge time then the energy in each battery can be estimated.
Another variable in the test is the discharge voltage at which we decide the battery is exhausted for which we have chosen 1V. This is on the low side, but it ensures that the battery is almost completely exhausted when the experiment is complete. In doing this we have accepted that we will always be slightly over estimating the usable energy in the battery, but the choice allows for side by side comparisons of other lower voltage battery types like Lithium or NiMH, and will provide consistency.
These two sets of charts below are for AAA batteries and AA batteries respectively, The Gold Colour are for Alkaline Batteries from various manufactureres and the red colour are for Zinc Chloride batteries again from a variety of manufacturers. Alkaline batteries are generally preferred for high power applications and as you can see they have a higher charge.
| AAA Batteries Charge (Milli Amp Hours) | AAA Batteries Price per unit of charge (Pence per Amp Hour) |
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| Results based on our experiments. [ Number in square brackets is the number of batteries tested ] |
Results based on our experiments and the average price paid in UK shops or online for these batteries. [ Number in square brackets is the number of batteries tested ] |
| AA Batteries Charge (Milli Amp Hours) | AA Batteries Price per unit of charge (Pence per Amp Hour) |
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| Results based on our experiments. [ Number in square brackets is the number of batteries tested ] |
Results based on our experiments and the average price paid in UK shops or online for these batteries. [ Number in square brackets is the number of batteries tested ] |
The Circuit
The circuit used to test the batteries is below, Vlow and I are set using a digital voltmeter.
Some Operational Notes
- Vlow is chosen, the voltage at which the battery is regarded as exhausted, we have chosen 1V
- A discharge current is chosen and set
- The clock is set to zero
- A test battery is inserted
- Mains is switched on
- When the clock stops calculate the number of Ah (amp hours) = Time in hours X I (the current)
- e.g. if time is 20h and current = 20mA this gives 400mAh
To the right is a picture of some of the AAA batteries we have tested so far, the numbers on sticky labels indicates the number of hours the battery lasted in our tests.
It is becoming quite clear now that the chemistry of the battery is much more important than the make. Almost all the cheap brands performed as well as the brand leaders, and they cost significantly less. Cosco, Tesco and Ikea batteries perform as well as any, we were pleasantly suprised, so here is a good way to save some money.
