I want to run a cable from my main battery to an Anderson connector in the cargo area of my 2005 Subaru Outback, to support charging a secondary battery. The secondary battery will be in a removable battery box so I can take it out for camping.

I will put an inline 40A fuse near the battery. The battery will be charged via a 20A DC to DC converter.

What is the best route for the cable to take from the battery to load area?

What is a good grounding point in the load area for the other terminal of the Anderson connector?

2 Answers 2


Why waste efficiency with a dc to dc converter? Just use a split charge relay. Used for caravan second batteries and also winches.

As for running the cable, follow the esisting wiring going from front to rear - they considered all the issues when they planned the route.

  • I'm going to be using an LiFePO4 battery, and the DC-DC converter has some charging smarts in it too.
    – tgdavies
    Oct 27, 2021 at 4:20

First, ensure you are using the correct wire gauge by using a tool like the Blue Sea Systems Circuit Wizard. This will make sure you don't waste money on too large of a cable, or create a fire hazard with too small a cable.

Second, try to find a fuse closer to the current draw, like a 25A instead of double to ensure a short on the wire will immediately pop the fuse.

As far as a ground point, any large bolt on the frame should be sufficient, assuming your battery ground cable is large enough to carry an additional 20 amps. If not, you would be better off to install a larger battery ground to frame cable. I agree with Solar Mike on routing - follow a factory wire harness. For an extra measure of safety I'd also suggest putting the power cable in a wire loom to keep it safe from abrasion.

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