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Wednesday, December 9, 2015

Replacing the Prius 12 Volt Battery

My Prius 12 Volt (AGM) battery has been getting weaker over time.  I monitor my Prius 12V battery with a digital volt meter tied directly to the battery.  My Battery is original to my 2011 model year Prius, so it is 5 years old.

When I returned from my 2015 travels the resting voltage was down to 12.7 volts from a start of my trip of 12.9 volts.  I decided to wait out the summer and consider replacing it in the fall.  This morning I checked and the Prius has sat for a number of days in not too cold temperatures and it was down to 12.4 Volts. There is always some parasitic draw from the Prius.  Just opening the car door with no cabin lights there are relay noises.

Although I run the Prius enough during my travels that I should expect to get buy for my upcoming travels with the existing battery, I wasn't ready to risk it.  There is too much is riding on the Prius 12 volt battery living off grid.

Note:  In an emergency I do have a back up strategy as I can backfeed my house 12v battery setup to assist the Prius 12 volt battery.

After considering all these factors I made the decision to replace the battery today.

I went to a dealer who had a reasonably priced OEM battery with an October date code so I bought it.

The next step was to slide off the housing I made above the battery in the rear passenger hatch area where I house my 400 watt pure sine wave inverter and expose the old battery.

I removed the hold-down bracket and power leads and swapped out the battery.

Many ask questions in online forums about venting batteries.  Here is the disconnected AGM battery vent tube that vents through the floor of the vehicle.

Here is the view of the vent tube reinstalled in the side of the new battery.

 With battery cables reinstalled I placed my Prius 12 volt battery area back in place over the battery.

With the Prius connected to shore power I have the new battery on the BatteryMinder  conditioning charger.

Another item done for 2016 Travels.



  1. Hi Brent,

    Just wanted to say how much I've enjoyed reading your blog. Found you from over at the Cheaper Living Forum. You have lots of great tips in here and like how your Prius is setup. I'm looking to get a cargo or conversion van but the gas mileage is great for you!

    Looking forward to following along on your travels.

    Northern CA

  2. Tina

    Thank you for the feedback. Yes the cross country fuel costs forced the change to the Prius. When I first started off with the Prius I wondered if I could live in and out of it at about 6' tall, but I was able to get it to work even in stealth at times. Best wishes on the cargo van. I think it would be fun to modify with what I've learned.

    Enjoy the holidays,