Rechargeable Battery for iRobot Looj Models 125, 135, 155 Full Specifications
Ni-MH or Ni-CD,7.2V, capacity can be chosen use with Charger.  Easy to pop in and out of the battery compartment.
 

Fit with:
 

iRobot Looj 120
iRobot Looj 130
iRobot Looj 150
iRobot Looj 12101
iRobot Looj 11200
iRobot Looj 8482
iRobot Looj 2874294
iRobot Looj 2874296
iRobot Looj 12701