The battery light will come on for both NO charge from the Alternator and EXCESS charge(hi voltage) to the chassis 12 volt system. When this happens, do you have the Genset on also? When it happens try turning the headlights ON(if they are off) and the Dash AC ON if it is off and see if the light goes out. This puts a higher load on the system and if too high voltage, it will drop the current about 1/2 to 1 volt. If on Genset, the Inverter/Charger if you have one may be in BULK charge which will send a higher voltage to the chassis system until the Inverter/Charger goes out of bulk charge. Did you replace the Alternator for the same problem? Doug