This is not new. You'd encounter the same thing from any other car dealer if you brought your vehicle in for a charging system problem and they discover you've been pulling 100+ amps continuously(1200 watts at 12 volts = 100amps) from the system.

Vehicle alternators(the device that charges the battery while the engine is running) are not designed to continuously output that kind of load and would likely be damaged if it were used for any significant duration at that load.

I have done this myself with a non-electrically propelled vehicle and have damaged(due to overheating) an alternator in the process.