Lithium Polymer (LiPo) rechargeable battery was initially designed for RC toys but eventually become so popular in robotic sector due to its small-size and lightweight. But it is relatively hard to maintain and may explode if being misused.

Specification:
Ordinary Voltage: 22.2V
Fully-charge Voltage: 24.2V
Capacity: 500mAh
Discharge rate: 35C
Able to use for most of the 24V controllers, motors or any other appliances
Must charge with designated LiPo Battery Charger
Please check Wikipedia link about Li-Po Battery.
Dimension: 55mm x 30mm x 30mm