The tax credit expires on Dec. 31 and it's based on the "in operation" date of the equipment, not the date you purchase it, so it's likely you're probably already too late to get it unless you can buy it, have it delivered, installed and functioning in the next two weeks (good luck with that).
WRT electronic ignition - true, but
AFAIK you can run that off a generator. A full-blown electric HW heater, not so much (or buy a MUCH bigger generator).