I have a 2013 Ford Edge Limited all wheel drive which I tow 4 wheels down. Although I follow the manual; key in accessory position, shift in neutral, stop every 4 hours or so and run the engine 5 minutes, at the end of the day (8 hours of driving), the car battery is dead. I am reluctant to pull the fuse for the ignition (No. 28 per Camping World and other sources) since I do not know what it might affect (e.g. odometer, radio settings, etc.). I have been told to run a charging line from the motorhome to the car battery. Is it best to have something like a Towed Vehicle Charger by RV Brake installed or just a direct line without a controller to prevent overcharging. Recommendations.
I'm not sure over charge is a problem. My factory install is a direct line from battery to an ignition controlled relay and through a fuse. We had same problem with our Acura until I connected to the charging circuit. I do not think it would be hard to install.
The one time I towed the Acura mdx all day with the headlight switch in "auto", we ended the day with a dead battery. No problem ever with the headlight switch in the "off" position.
Could have left the ignition switch in the on position instead of accessory. Easy to do and you would not be the first.
PIerce
I tow a gmc Terrain and have to pull a fuse to keep the battery from discharging. I got a fuse switch so all I have to do is flip the switch and not worry with the fuse. No milage on car when towing. Put in a fuse switch and follow instructions. DAN
It would be easiest to get a cheap solar panel that sets on the dash and plugs into the cigarette lighter. It will never over charge and you can use it for other things.
Use LSL Toad Charge TOAD-CHARGE Dinghy Vehicle Battery Charger/Maintainer (http://www.lslproducts.net/ToadChargePage.html). We have it, even though we don't have to leave our Jeep ignition key to tow, and several other Foretravelers use it.
Same company makes the very popular Trik L Start.