Just looked at Ed's reply and he is right about voltage drop. What I do is check each cell while in tilt bypass. You should be able to locate the bad cell or cells that way.

Just looked at Ed's reply and he is right about voltage drop. What I do is check each cell while in tilt bypass. You should be able to locate the bad cell or cells that way.

How long have you had the units? I have seen factory settings be wrong for the trucks and adjustments need to be made for the type of battery in the truck. Do you equalize charge your batteries?

Ok thanks. Ill go over the batteries again.

it may well be both units have bad batteries. it takes more power/current to lift to dead head than to lift and drive.
As I use it here, "phase" has to do with the AC input lines, (sometimes called the mains) and includes the input line fuses and should be an voltage equal reading between any 2 of the 3 main lines if it is a 3 phase AC, and that number should be at the number the jumpers are set at.
As far as how you read it; with one hand in your pocket and with training in how to work on AC power lines (might be a good time to call an electrician, if in the USA, for insurance reasons).

Just lifting dead headed would be more around 78-79 volts. I've never checked chargers. Does phase have to do with where the jumpers are installed? How would I check the input power?

I know there are twin units there with different batteries and chargers. They are having the same issue with both.

there are settings in most BDIs to set for the "ramp" of the discharge, but if your battery drops from 85 VDC at rest to 71 vdc under load (and don't try to read it when moving, just lifting to max lift and hydraulic stall for less than 4 seconds) you have a bad battery, or at least a bad cell. (10% voltage drop=needs battery checked [85vdc minus 71vdc= 14vdc > 8.5vdc=10% of 85vdc])
is your charger a 3phase A/C, and are all 3 phases equal input power?