Installed Battery Disconnect Switch In Prius

Apparently there’s enough parasitic draw on the battery of our 2008 Prius to drain it over a 2 month period.

Just like 2013, when we came back home this March after being gone about 2 months – dead battery again.

I asked a Toyota service department if it was safe to connect a low current battery tender to the car when we’re gone. They felt it would be fine but said some customers simply disconnect the negative battery lead. Um, easier said than done.

I had a battery disconnect switch and some pre-made cables in inventory from past Car PC and Car Stereo installs. All I needed was some 1-1/2″ nylon screws.

The battery is a bit bigger than a motorcycle battery. It’s in the trunk area inside the passenger rear fender well and it is buried!

Completed project:


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  1. Jim, I think the keyless entry/ignition may be the main component of the parasitic drain. On our 2005 Prius, there was a control sequence (see owners manual) to turn it off while in airport parking lots or away for an extended period.

    But a cutoff switch takes care of it and might be easier to use.

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