Hi!
Of course when I'm in a hurry the robot's batteries fail... We bought this robot used and someone had put basic 3.0V CR123A lithium camera batteries in to backup the encoders. I changed them to similar ones (around 1500 mAh) and they lasted only half a year.
I don't have the robot manuals. Based on the battery holder the original batteries must have been size C. I'm wondering which battery type is the correct one because 3.0V C size batteries are not that common (they are usually 3.6V). Maybe the original ones were C size 3.6V and someone has put wrong voltage batteries in?