Why Cant a Trailer Battery be Charged through Trailer Connector 12 Volt Circuit

Question:

I have been advised by your experts that my truck will maintain my camper battery truck mounted but will not charge the battery. Is there a difference? Is there a way to charge the Camper battery while driving the truck the next day after a night of dry camping, using the 7 way attached plug from the truck? When you say the truck will maintain the Camper battery does that mean that if the Camper battery has 12.5 volts in the morning after dry camping the previous night, that the truck will maintain the 12.5 volts during the next 10 hours of travel or whatever, but will not increase the 12.5 volts to the normal full charge of 12.8 volts? What can I do to charge the battery in my Camper while driving my truck?

asked by: Roger G

Expert Reply:

In nearly all cases, the 12 volt circuit in a trailer connector and tow package wiring, cannot charge up a trailer mounted battery (unless its a breakaway battery). The issue is that the wiring is too small and the alternators on most vehicles are not strong enough to push back the amperage required to charge up the battery.

The low amperage 12 volts coming through the trailer wiring can keep the battery from draining but to charge up the battery I recommend connecting it to an AC charger when you can. Several of us here use CTEK charger # CTEK56353. It works beautifully. It will not overcharge a battery and it can help to recondition a battery so it lasts longer.

And of course trailering veterans will tell you; always carry a spare!

expert reply by: Michael H