A few years ago, I installed a Renogy DC-DC charger for improved charging power from my truck alternator to my trailer batteries. My truck has an optional 220-amp alternator, so I was able to go with a 40-amp DC-DC charger. It’s worked out great and allows me to recharge my lithium RV battery bank as we drive to the next campsite.
At the time, I received several questions regarding the regular 7-pin tow cable and its charging wire. Also, many people wonder about using lithium batteries in the trailer and whether that will harm the alternator since they have the potential to draw more amperage than lead-acid.
Since I was about to swap out my old 7-pin cable, I decided it would be a good time to do some tests so folks could see firsthand the amperage drawn through my truck’s trailer battery charge wire. My pickup is a 2018 Ram 3500 with the factory tow package and fifth-wheel prep option.
7 Pin Tow Cable Battery Charge Test Video
As you can see from my tests, the actual amperage drawn through the 2018 Ram truck’s charge wire is pretty low at about six amps or less. This is due to the very long wire run and its relatively small gauge, I’d guess about 12GA. WARNING: Vehicle charge systems differ, so look up the information for yours and/or do some tests.
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