Low voltage can cause problems with electric brakes. A fully charged battery should operate this truck for six to eight hours, unless you are doing an excessive amount of lifting. What was the voltage when this "new" battery was installed; and what was the voltage when the problem reoccurred?
Brake clearance can also be a problem. The gap between the coil housing and the upper pad assembly should be.23 -.58mm. When the brake is released the measurement above and below the rotor should be nearly equal (.o51-.533mm)
There could also be several problems with the brake control circuit.