I tow with a 2019 Ford F-150 and have the 640 AH lithium batteries. Sometimes (not always) when I start my F-150 when towing the truck has a weak crank/battery but (so far) always starts. Since I have 640 AH lithium batteries the truck alternator is not used to charge the batteries. The running lights of the Oliver do draw the charge from the truck, but seems unlikely being enough of a draw to weaken the truck battery. The truck battery is less than two years old and tests Ok.
So, what are the potential causes of the towing truck weak battery{?} and weak start cranking? Need larger battery? Need new or alternator or high capacity alternator? What is your guess? Has anyone else experience weaking starting crank when towing an Oliver Travel Trailer?