1. Unless your add on charger goes OVER 14.2 or so volts, no damage will happen. Lets take charger at 14.2 volts. The 14.2 volts will be seen and transmitted to all DC lines and appliances.
2. AMPS is the work term. Very doubtful that any extra charger will supply MORE than 40 or 50 amps. Probably closer to 2 to 20 amps as most aftermarket battery chargers run in that range
3. NOW, a responder stated an equalization charge up to 16 volts. YES, the ideal is to DISCONNECT all loads(12 volt appliances) when doing a Equalization charge and the Manuals for chargers that can do equalization state to have NO 12 volt appliances connected when doing the high dc voltage charge. Sustained DC voltages OVER 14 volts can damage some DC appliances. Doug