Charging A Trailer Battery From The 7-Way 12v Power Pin And Preventing Feedback

Question:

I have an AGM starter battery in my tow vehicle. I am installing a new lithium battery in my travel trailer. I am concerned the higher lithium voltage will try to charge my AGM battery and possibly harm it. Since I previously wired the 12v accessory wire on my 7-pin directly to the battery positive, should I disconnect it, or is there a product diode? that will prevent the AGM battery from draining the Lithium battery while driving? Thanks.

asked by: David A

Expert Reply:

The battery type doesn't matter in this situation as you could still face this issue with two AGM batteries. If you're vehicle is running the alternator should be charging the start battery more than the draw from the 7-way 12v accessory pin. As long as the alternator is properly functioning you shouldn't have an issue charging both batteries while driving.

If the vehicle is off and the 7-way isn't tied to the ignition for power then you run the risk of draining the start battery if you're still connected to the trailer. You can install an isolator, like part # DW08770, to prevent the trailer battery from drawing on the start battery while the vehicle is off. You'll want to check the amperage of the alternator before purchasing an isolator, you'll want to go with one that's higher than your alternator's amperage. You can also install a diode like part # RM-690 in-line with the charge wire running to the battery to prevent any feedback.

expert reply by: Kevin C