A bit of further information that might help. Fresh off the charger the battery was at 39.3V then after moving the forklift back and forth a few times, I re-checked the voltage and it had dropped to 38.8v. A 0.5v drop in voltage for the very little amount of work, seems a bit excessive to me.
Is it possible the battery has a cell that is fading/dying and the voltage drops too rapidly under load for the machine to function properly?
Now the error code is just showing 6X Inform Service. Does this code correspond with the symptoms of a faulty battery?