Yah, we need more details...

If it has ev100LX then the bdi is controlled through the traction card, and can be adjusted somewhat.
A straight ev100 non-lx will have a curtis bdi assembly that can also be adjusted for cutout and reset.

(the difference is the display, only the LX trucks have the little led display that shows hours, codes etc.)

I suspect the problem is simply the reset voltage.
The bdi's won't reset to 100% until the battery goes over a certain voltage. If that voltage is too high, or the charger shut-off too many hours before, the guage won't reset.
Just reset the charger, and after a short time (10-30 seconds) unplug the charger and quickly plug the battery into the truck.

If that fails to solve the problem, we'll definatley need more info...