Recommendation for Charging Trailer Battery from Towing Vehicle

Published 02/15/2018

Products Featured in This Question

40 Amp In-Line Circuit Breaker - Perpendicular Mount Bracket

(100)

$9.95

Redarc In-Vehicle BCDC Battery Charger - Dual Input - DC to DC - 12V/24V - 25 Amp

(90)

$535.00

Question:

Hi - Can you explain why there is a difference between maintaining a battery from a 7-way and charging it directly from the vehicle battery - I want to charge a deep cycle agm 75ah and want to know if I can go directly from my 7-way in truck bed to the agm aux battery - Or do I need to add a dc to dc Trickle charge unit between the two. Thx

asked by: Koral

Helpful Expert Reply:

You can connect your deep cycle AGM 75AH trailer battery directly to your 7-way 12V power for a small maintenance charge. This normally will only give you about 2-4 amps charge because your vehicle is needing the other amps produced from your alternator to maintain your vehicle functions. Only what is not used by the vehicle is available for the trailer battery. This also will not allow a full charge to your battery but will charge it up to about 80% just like a trickle charger, where a charger and maintainer would allow full charge. For this, you will need to use a 40 amp circuit breaker like # 9510 if your vehicle doesn't already have a circuit breaker in line for that charge line.

The DC to DC chargers are able to amplify the signal from your 7-way. So you can use different chargers for different amperage charging. For instance, the RedArc BCDC charger # 331-BCDC1225D will provide up to 25 amps continuous output to charge and maintain your battery. This will provide a much faster charge and up to 100 percent charge on your 75AH battery. I've attached a video to assist.

The biggest difference is the amount of time to charge and the percentage of charge. A DC to DC allows you to charge on the go, where the 12V basic connection really doesn't do much for charging unless you are traveling a really long distance but it may be all you need depending on your use. Let me know if your have further questions.

expert reply by: Jason S