I have a 2500 Savanna (GMC, 2001, extended), with an entertainment system. The stock battery is fairly small, and I don't want to run the engine or drain the engine battery when playing videos for the kids.

I have an unused, new lead acid battery (from a 2000 Ford windstar - big battery). While it's not a deep cycle battery, I'd like to use it as an auxiliary battery. Primarily to power the entertainment stuff, but on occasion to jump the engine if for some reason the engine battery is dead.

How do I go about doing this?

2 Answers 2


What you are looking to purchase is a electronic battery isolator kit. What it does is allows you to add an extra battery which stays separate (isolated) from your main battery. When the vehicle is running, the isolator charges the primary battery first, then when it's full, it will charge the auxiliary battery. When the engine is cut off, the auxiliary battery is kept separate and allowed to power your extraneous devices, like your entertainment system, without draining your primary battery. There is a side benefit to doing this, as with a flip of a switch, the auxiliary battery can be used as a power source to start your vehicle. Here is a YouTube Video which explains it very well.

I don't know enough about them to recommend any specific isolator, but this guy has a pretty good write-up about the Enerdrive VSR system. I am not recommending it personally, but would suggest you get one with similar attributes.

I believe you'll need the isolator, some cabling (you'll have to figure out which gauge you'll need - also remember that the longer the run, the larger gauge you'll need to compensate), the battery (which you already have), battery tie down/mounting point, and connectors. I'm sure there are plenty of kits which you can purchase which will have everything besides the battery. If using a standard lead/acid battery, you do not want to mount it within the cabin of the vehicle, as it produces gasses when charging/discharging which can be hazardous.

  • Try looking at a camper or caravan dealers/suppliers to see the bits and pieces needed. You might also be able to get a ballpark figure for costs. Commented Sep 25, 2014 at 18:43
  • These isolators also work rather nicely if you have an old car and its mechanical fuel pump goes out. Since they only provide power when the engine is running they make a reliable way to ensure that power to a new electric pump gets cut off in the case of an accident so you don't pump fuel all over a hot engine block. Generally does need a bypass circuit to run the pump for a couple of seconds for starting, but that can be a simple push button added to the dash.
    – Perkins
    Commented Nov 8, 2016 at 21:04

I would also add in a one all two battery switch so that you can isolate your battery usage to the One battery instead of using all the voltage out of the truck batteries so just in case you do use too much voltage and it drains that battery you could always switch to the other ones and start your vehicle and then you can switch it to all the charge hole system I would just make sure that your alternator you have in the vehicle is able to produce enough amps to charge all three batteries or two batteries it's something that you need to look in your vehicle diagram so that you don't bring your alternator out your vehicle

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