Fuelband Battery M, L, XL (set of 2) 3.7V 43mAh upgrade from 36mAh. ***36mAh replacement only*** Battery Replacement Fuelband Nike, may not fit size small band, check to confirm 36 mAh This is a DIY kit with instructions included. For complete replacement service, to have the batteries changed for you go to BatteryReplacement.Co and ship us your Fuelband.