mAh refers to the length of battery life (milliamp-hours).
Take an amp that uses 20mA steadily. If the battery was rated at 20mAh, it would last one hour before needing to be recharged. if it was 200mAh, it would last 10 hours. 2000 mAh, 100 hours.
In reality, the battery drain of an amp fluctuates depending on the volume and dynamic range of the music, but it's usually possible to calculate an average.
P.S... in the case of battery packs (more than one battery of the same mAh wired in series) you would use the mAh of a single battery rather than adding them all together. So a 16-cell battery pack using 1.2v 1800 mAh "AA" cells (supplying 19.2v) would have a lifespan of 1800 mAh.
Originally posted by penbat Thanks. Can you undestand why a battery maker offers a 9V battery with a high mah and another 9V battery with a low mah for the same price ?
The battery with lower mAh is probably just older technology, but for whatever reason was never reduced in price. Also, brand probably has something to do with it... well known name brands tend to get priced higher (and *might* be better quality, depends). Also, highly rated brands (by buyers) also tend to get priced higher.