It's a 4 cell lithium ion battery, 2200 mAh. It has an internal protection circuit that provides individual cell protection, as well as over charge, under charge, and overcurrent protections in case anything goes wrong in the D180. In normal conditions, the D180 manages it and keeps it charged.
The door for the battery is on the side of the D180. The battery fits inside.
The battery will last at least 2 hours running the D180 and an average load of sensors.