Protecting Vehicle Battery from Excessive Draw from Trailer Battery

Updated 03/24/2015 | Published 03/22/2015

Products Featured in This Question

Starter Solenoid - SPST - 12 Volt - 100 Amp - Continuous Duty - Grounded

(14)

$35.41

CTEK MULTI US 7002 12-Volt Universal Battery Charger w/ Pulse Maintenance and Backup Power

(98)

$199.99

Firestone Fuse Circuit Tap Kit

(41)

$22.03

Question:

Im a little concerned about my camper trailer battery drawing too many amps from my vehicle battery if my camper trailer battery is low on juice. The breaker should help, but is 40 amps low enough to protect my vehicle from damage? That seems like a lot of current through a 10 gauge wire. Thanks!

asked by: Jeremy

Expert Reply:

The best way to ensure adequate power for your towing rig is to fully charge both the vehicle and trailer batteries before heading out. A simple tool like the CTEK MULTI universal charger # CTEK56353 will work on both your vehicle and trailer batteries to "top them off" before you head out. This charger has specific modes for both smaller batteries and for car batteries.

If you want to have a fool-proof way to avoid the trailer battery from draining the vehicle battery, you can install a Tow Ready Battery Isolation Solenoid # PK5231201. This uses a 12V trigger signal from your vehicle (using any ignition-controlled circuit, such as a power antenna) to stop the flow of power from the vehicle to the trailer when the ignition is turned off. You'll use a fuse tap like Firestone # F2526 to get the trigger signal. The photo shows how the solenoid wires up in your truck.

A circuit breaker will not give you the isolation you need to protect your 4Runner's battery.

expert reply by: Adam R