AG10 batteries are alkaline button cell batteries used for small electronics.  To know if your device uses an AG10 battery, the old battery will usually say AG10, SR54, 189, 387, 389, 390, LR1130, or SR1130 on the battery.

Single AG10 Button cell battery

Best Deal
AG10 Batteries on Amazon

The best deals on AG10 batteries will be sold in card packs of 10 batteries online.  One card pack of AG10 batteries will normally costs less than buying a single Energizer battery at the store. 

Battery Specifications
AG10 Batteries are 1.5 volt batteries with a diameter of 11.6mm and a height of 3.1mm.  The capacity of the battery ranges from 44 mAh to 68 mAh.