system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why are battery capacities expressed in Ah (Amperes-hour) and what does it mean, for example, a AA battery that is 2500 mAh?
gpt
Theoretically, an amp-hour is a battery's ability to provide 1 amp for 1 hour. Or 1/2 amp for 2 hours. Basically, an amp-hour makes the equation *time* x *power-draw* = *amp-hour*. We use this because drawing more power from the battery makes it run out faster, but the actual storage wouldn't change.

In practice, the chemicals and materials in batteries are optimized for a certain draw. So a small battery (AA) with 2500 mAh that is optimized for 50 mA would last about 50 hours, but if it is ran at 200 mA it might only last 10 hours instead of 12.5.