Standalone Second Battery for assesories

Luke Millard · September 17, 2020

So, I think this is a obvious question but I would like to be sure im not missing anything. I want to add a auxiliary battery to my 09 silverado but after looking into the system I would really prefer not to mess with both the cost and wiring of a traditional two battery system with a isolator. I was wondering though is it un reasonable to just throw a deep cycle battery and wire what I want to it (bed lights, 12v ports in bed, maby a few others) and then basically have it as its own electrical system with nothing connected to the first battery or grounded to body? I could then just use a charger to recharge it when it died? If anyone else has any other similar system or other ideas any help would be appreciated. I've also considered just hooking everything to a low voltage disconnect but I assume I would not get much use from just that.

Thanks!

Edited September 17, 2020 by Luke Millard

TomDiesel · September 17, 2020

The idea of using a separate battery to power lots of neat electrical stuff, but not drain the battery you need to operate your truck has a lot of merit, and has been done before. In fact, the separate battery attached to the truck battery by an isolator diode is the simplest solution. Having to recharge a deep discharge battery when it dies is a lot of work. After all, how do you know when it needs recharging? Then there is the connecting and disconnecting the charger (After opening the hood, of course).

Using the isolator guarantees the separate battery will always be recharged once you start the engine. Let me explain. A vehicle battery is considered charged up when it is at 12.6 Volts DC with the engine off. Your alternator puts out a voltage greater than 14 Volts DC when the engine is running (How high depends on battery state and other elecrical demands). The isolator diode will charge the separate battery once the charging voltage is greater than 0.6 Volts DC greater than the separate battery voltage. If the separate battery had been discharged down to 12.4 Volts DC, that would happen at 13 Volts DC.