Do you have the new motherboards in the pumps with the larger pins as we did find that the small pin motherboard had a tendancy for the pins to stick. Solution was contact cleaner and a cotton bud or the replacement of the motherboard.
If you also go into the service software and run the battery test and you can see what the mAh of the battery is.
As for the perfusor model make sure the drive arm guides are not out of the retainers as this will make the arm crash drawing a lot of current and giving you the error with the battery.
Have you tried a known good battery in the offending pump.