Recommended Way to Charge External Battery Using Tow Vehicle Battery

Question:

As noted below Jeff recommends a CTEK MULTI US 7002 12-Volt Universal Charger, - Got it. What is the technical problem with using a 12V to 120V inverter to provide 120VAC power for the CTEK 12V smart charger. This of course would only be used to charge while the truck engine is running to charge a 12V 55Ahr AGM Battery. Expert Reply from Mr Jeff L. The battery on the trailer will not charge if it is attached to the 12V power wire from the towing vehicle. It will provide a small amount of current that helps maintain the current charge of the trailer battery. I recommend using a battery charger like the CTEK MULTI US 7002 12-Volt Universal Battery Charger, part # CTEK56353. This charger features pulse maintenance and will not overcharge the battery like many of the common chargers do.

asked by: Dave S

Expert Reply:

Technically you could use a DC to AC converter like part # WC3720 with the CTEK MULTI US 7002 # CTEK56353 to charge an AGM battery. The only benefit of doing this though is having the ability to easily remove the CTEK charger and plug it into a wall outlet. Since the initial power is coming from the battery on your vehicle you would still get that trickle charge meaning your battery wouldn't charge at a fast rate.

If you plan on leaving the CTEK converter on your trailer though then the best and easiest way to charge your battery is by using a DC to DC charger/maintainer like the Redarc In-Vehicle BCDC Battery Charger # 331-BCDC1225D. This option not only allows you to use the trickle charge from your vehicle battery but it also allows you to add a solar panel like part # 34273836 to the mix for a faster charge time. You don't have to worry about extra connections with each converter and and you have the charger and maintainer combined in one unit.

Attached are some installation and review videos that you can reference.

expert reply by: Jon G