Isolating Auxiliary Battery From Draining Break Away Battery

Question:

I am going to add an auxiliary battery to power my winch in my cargo trailer. I want to maintain the battery change when driving and keep a battery tender on the battery when it is not in use. My question is do I need to isolate the breakaway battery? I don’t want the breakaway battery to drain itself when I am using the winch. I still want the breakaway battery to charge from truck while it is running but I don’t mind if the breakaway battery doesn’t charge from the battery tender. If it can cool if not no worries.

asked by: Mike

Expert Reply:

You can isolate the break away battery from the auxiliary battery using the Battery Isolation Solenoid # PK5231201. The auxiliary power supply that is needed on this solenoid can be the running lights of your trailer. That way, when your trailer is connected, you can charge the break away and the auxiliary trailer battery, but when not connected the break away battery will not be drained by the auxiliary trailer battery. So the 12V comes into the trailer and runs to the aux trailer battery which then runs to the breakaway battery with the solenoid in between the trailer battery and the breakaway. This allows the trailer battery to be charged and to charge the break away battery, but the disconnection of the running light circuit to the auxiliary pole of the solenoid will not allow the trailer battery to pull power from the break away battery.

If you have a small enough amp battery on your trailer, you could just us a diode like # RM-690 that is rated for 12V at up to 85 amp. You could just run this between your trailer battery and the break away battery.

expert reply by: Jason S