Dinghy charging from MH

theoldwizard1 wrote:
The only way you will ever be able to maintain/charge a "toad" battery is with a DC-DC charger. Have it permanently mounted in the toad, close to the battery. You can pick up B+ from the tow vehicle via the standard 7 pin connector.

You need to be ABSOLUTELY CERTAIN that B+ from the tow vehicle does NOT connect to B+ of the toad ! Thus way require some relays to keep these two systems isolated ! Using separate brake/turn signal lamps is a good first step !!

Have to respectfully disagree with this, based on what I've experienced and learned over the years.

I've flat towed a total of 4 different vehicles over course of last 10 years. Two of which (Ford Fusion Hybrid and Ford Taurus) were such that battery would be dead after just a few hours towing.

I installed a charge line several years ago. Basically, just a wire going from + of Motorhome battery to + terminal of towed vehicle battery with a 20 amp inline fuse (what you are saying should not be done).

To be clear, I did not physically run a new wire from the Motorhome battery to the towed vehicle. The wiring on the Motorhome side was already there somewhat, by using the auxiliary power line in the standard 7 pin connector at back of the Motorhome. After verifying that 12V power is always on that line when Motorhome is running, I just used that and wired it to the + terminal of towed vehicle battery.

And, it has worked great all these years, on all the vehicles I've towed. Kept the battery well charged up, on vehicles where the battery would die in just a few hours of towing without the charge line.

Wiring in a DC charger definitely isn't a bad idea, especially if you have something that will put a huge load on the towed vehicle's battery (like maybe an auxiliary braking system that needs a lot of 12V power). However, I don't think its fair to say that is the only way you will keep the battery charged, as my experience over the years proves otherwise.