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  • Writer's pictureTrevor Fry

Fixing a Toyota Prius Battery

I've had quite a few cars in my time, one of them being a 2005 Toyota Prius with a bunch of miles on it. The Prius gets ragged on a lot for being what it is (a slow, kind of funny-looking hybrid), and I was one of them even during my ownership (why does it beep inside the car when you go in reverse?!). However, looking back, it was a solid little car that got some great mileage.

Well, solid except when the Red Triangle of Death popped up one morning. You are more than welcome to do your own research, but to summarize this big, bright red triangle light (among others) glows when your hybrid battery starts dying. This will likely leave you unable to drive so when it happened to me, I darted home and got it in the garage until I could figure out what to do.

As it turns out, when this happens you have a few options:

  1. Buy a whole new battery from Toyota ($,$$$)

  2. Buy a refurbished hybrid battery from a 3rd party ($,$$$ but less than new)

  3. Tear apart the existing battery and replace the cells that are dead/dying ($$-> $$$)

Considering my love of taking stuff apart, a background with electronics, and not wanting to spend a few thousand bucks, I started taking the car apart.

DISCLAIMER: This is not intended to be instructional, nor would I encourage everyone to try this. These batteries contain potentially lethal amounts of voltage; please work with professionals to accomplish this if your battery is having issues.

There it is, the 40lb behemoth of a battery (well, really, 40lbs of little batteries). It was surprisingly easy to get to it; I want to say it took maybe 30 minutes to remove all the panels.

Next step, get it over to the bench (which was surprisingly not covered in crap here), take off the shell, take off all the bus bars (the orange and copper connectors between each cell), and start testing the individual cells to see which ones needed to be swapped out. Basically, you take a multimeter and see which ones have voltages that are not like the others.

If I remember right, I ended up replacing 4 cells with some "new" ones (probably out of a junkyard) I got off eBay. In all my excitement, it looks like I forgot to take a picture of the individual cell, but here's one if'n yer curious.

While waiting for those to arrive, I scrubbed the oxidation off the bus bars to make sure they were nice and clean.

To swap out the cells, you have to de-compress the pack by undoing these long bolts that go through the entire length and manually pry the packs apart to be able to get enough room to pull out a cell. I think the hardest part of this whole process was getting the new ones in and clamping it back together.

Once that's done, I used a battery tender to slowly deplete any batteries that were high, and charge any batteries that were lower to all be the same voltage over several days.

Not to pull a 'Rest of the Fucking Owl' here, but apparently, I didn't take any pics of the reassembly. It really is just doing everything in reverse though; put the shell back on, install it back in the car, put the orange, safety-plug back in, and give it a test drive.

I'm happy to report, that it took care of the Red Triangle of Death, and I drove it for several more months after that. Friends of ours ended up buying the car, drove it several hundred miles north to Portland, OR, and still use it regularly. The triangle did end up coming back for them after a year or so of ownership, and I believe they ended up buying a whole refurbished pack instead of swapping out more cells, which I think was a good move as there's a chance you'd just keep swapping cells out until you replaced all fo them anyway.


Who's got 2 thumbs and makes a Gantt chart of their vehicle ownership?

this guy:

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