Preventing Trailer Mounted Battery from Draining Battery on Tow Vehicle

Updated 05/07/2013 | Published 05/03/2013

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

Question:

My trailer sat for 3 years if the small battery is no good on the trailer will it drain my truck battery overnight

asked by: Steve

Expert Reply:

A trailer mounted battery is typically maintained by the 12-volt accessory circuit from the 7-way trailer connector. If the accessory circuit on your 7-way is live even when the ignition is shut off, it is possible that the battery on your truck could be discharged. If shutting off the ignition shuts down that circuit, you will have no worries.

If the circuit is live with the ignition off, you can unplug the trailer, disconnect the 12-volt accessory circuit from the trailer mounted battery, or install a battery isolating solenoid like part # PK5231201. The solenoid is installed inline with the 12-volt accessory circuit. When the vehicle ignition is shut off, the power to the accessory circuit would be interrupted. Any of these three methods will keep your truck battery from being drained.

Once you get the battery replaced (if that is your intention), you can reattach the 12-volt accessory circuit to the positive terminal of the trailer mounted battery, but keep in mind that this circuit can be used to maintain a battery, but the limited wire gauge and distance from the truck alternator will prevent enough power from getting through to charge a dead battery. When shore power is available, you can use a charger like the # CTEK56353 to charge the battery.

expert reply by: Mike L