Can the 12 Volt Circuit from a 7-Way Connector Charge Up a Deep Cycle Trailer Battery

Question:

I have a 2004 Fleetwood Niagra popup camper with a deep cell 12V battery on the trailer tongue. The main wire harness is a 7 way male plug from trailer tongue that plugs into a female 7 way harness in the tow vehicle, a 2008 Toyota Highlander. 2 questions: 1-When the main 7 way trailer wire harness harness is plugged into the tow vehicle harness, is the deep cell 12V battery on the trailer tongue charging? 2-I use an 3000w inverter to get 110v source for my 110v outlets in the popup when needed for coffee, charge phones. In the past I connected the inverter directly to my tow vehicle battery, and then plugged the 110v 30 amp power cord from the trailer into the inverter to get 110v. When needed I would start the tow vehicle to charge the tow vehicle battery connected to the inverter. This year I was going to connect the inverter to the trailer deep cell 12 v battery and hope the deep cell 12 v would charge when connected to the main wire harness to the tow vehicle. I bought an extension for my 7 way wire harness connecting the trailer to the tow vehicle. I was then going to connect the inverter directly to the trailer 12 v deep cell battery, and hope that when I connect the 7 way wire harness from trailer to tow vehicle that the trailer deep cell battery will charge when the inverter is connected to and drawing off the deep cell. Will this work?

asked by: Gary T

Expert Reply:

If the 12 volt circuit on the trailer side 7-Way connector is wired to the positive battery terminal then it would receive a maintenance charge from the tow vehicle. However there usually isn't enough current in the 12 volt circuit to charge up the battery unless it is running through a DC to DC charger such as # 331-BCDC1240D.

If you connect your inverter to the trailer battery it could drain it since the 12 volt circuit alone cannot charge up the battery let alone while something is drawing power from it. You could end up depleting the tow vehicle battery that way.

I recommend using a DC to DC charger and/or having a charged spare battery available in case the main battery gets drained.

expert reply by: Michael H