on the curtis box, there should be a wire that goes directly to battery neg, a wire that goes directly to battery positive (maybe from the key switch), a wire that comes from the switches in the hydraulic control valve, and a wire that goes to the hydraulic contactor (if it is a contactor and not chopper controlled, if it is chopper controlled, that wire is the input to the chopper controller. there may also be wires to the BDI gage itself, but they don't count _here_.
To -test- to see if the curtis box is the problem*, you only need to jumper the 2 wires, the one from the hydraulic control valve and the one to the hydraulic contactor.
* the safety reason for a lift cutout has to do with preventing a -traction- controller "run away" condition that can happen with too low a battery, and not life of the battery, or some other reason, therefor it is never wise to completely remove BDI-lift cutout.
As good as the battery readings may seem, differences between -any- 2 cell voltages and spec grav should not be more than 10% of the voltage or spec grav.