I heard many different things how to check the condition of batteries, but nothing satisfactory. So I did some experiments, and these are my results:
- If the voltage of a 1,5V alkaline cell drops below 1,3V (open circuit voltage), most cells are of no use in flashlights, while they are of good usability if above 1,3V. However, this measurement is not at all times appropriate. Some cells of some brands are still usable in that condition. While other cells are unuable even with 1,35V.
- Therefore, the better measurement is to additionally measure the short-circuit current in these cases. Usable AA alkaline batteries had 1,3A or more here, while unusable had for example 0,5A.
- At least with my multimeter, it did not make any difference if I use the voltmeter function or the special voltmeter function for battery testing. It seems that, for practical purposes, the integrated resistor is too high, so that no meaningful difference between open circuit voltage and voltage with load is perceivable.
- New 1,5V AA alkaline cells have up to 8A short circuit current. Whenever checking the short-circuit current of any battery, be careful. Only check for 0,5s or less. If checking for a long time, the cell might explode.
- Regarding the performance in cold environment (3°C), a battery will malfunction if it has 1,35V open circuit voltage and 3A short circuit current (measured at 20°C). Your values may vary, depending on the battery brand you use.
In a nutshell: checking 1,5V AA alkaline cells with a multimeter. If the open circuit voltage is above 1,4V, the cell is usable. Else, check the short-circuit current additionally. If it’s above 1A, the cell is usable. All other batteries are of no use, at least for high power devices like flashlights and digital cameras.