[Michael C Henry]

When the voltage drops the current flow (amperage), goes up so does the heat generated. Ever watch a cordless drill when the battery gets low that's when they will burn up and smoke is bad. It's time to swap batteries or take a break and charge that battery.
I have my 4 fans ( two sets of two fans , 2-upper and 2- lower that cover the radiator) supplied by Bosch relays, battery current supplied to relays and control from adjustable thermostats and dash bypass switches to get ahead of the thermostats if anticipated.