12 Months Later

*Knock on wood* I have had absolutely no problems with the Prius. More than 25 000 km later and it’s as though the battery never gave me any trouble in the first place. There’s not a lot more to say about it than that, really. If the battery isn’t giving you any trouble, the car just drives. I don’t have any easy way of determining the pack’s health, and it’s completely possible that I’ve wrecked everything and shortened the lifespan of the traction battery, but it sure doesn’t seem to be the case. I have over 250 000 extremely rough kilometers on the car – I did construction and renovation projects to help pay for university, and used the Prius as a truck. I’m sure that contributed to the early wear of the battery pack, as there was an inordinate amount of dirt and debris in the car that probably very few other Prius in the world are subjected to. For example, I once filled the back with the waste shingles and roof debris from a re-roofing job. So that all said, I think the battery is probably one of the “healthier” pieces of the Prius as it stands right now. It’s missing most of its front bumper, and numerous non-essential pieces of the body. A small oil leak, a couple rust spots, but it still runs.

Would I do it again?

Absolutely. Particularly having done it before, but looking back, if I were doing it for the first time I still think it was well worth it. I very briefly thought about trying to set up a business offering assistance with other people’s hybrids, but I really don’t care enough to learn all I would need to do it properly. I’d certainly help anyone looking to do it themselves though. It’s utterly preposterous that the status quo is “sell us your old pack, we’ll sell you a new one”. I learned a massive amount, overcame most of my fear of electricity, and saved a few thousand dollars. I’m lucky enough to both work at a job that is very accommodating with allowing me to work from home when I needed to, and having a partner who was willing to ferry me around a bit. That bought me the ~1 month I needed to diagnose what was wrong with the Prius, research my options, buy everything I needed, wait for it to ship, fix the battery, and put it back together.

7 thoughts on “12 Months Later

  1. Fred


    I have Toyota Camry Hybrid LE 2015
    185 000 km I have battery fault
    Now I have 225 000 km
    We replaced 6 cells, but after 3 weeks the error comes agat. I am still able to reset it, but it comes to often if I am driving continuously in the city. If only work-home than no errors.
    I am in Hamilton Ontario
    Do you repair hybrid batteries?

    1. tobymurray Post author

      I have repaired my own hybrid battery in a completely amateur fashion. I have never repaired anyone else’s, and I’m not qualified to do so. I am open to playing a supporting role, but this whole endeavor could have ended with a dead battery easily enough.

  2. tobymurray Post author

    Hey Fred, when you say 6 cells I assume you mean 6 modules (the things that are pictured leaning against each other here: https://technicallyrural.files.wordpress.com/2016/07/dsc_0205.jpg?w=1920)? I’ve never tried replacing a single cell within a module – I’ve read that it can be done, but didn’t seem worthwhile for me. That’s a significant number of modules to have replaced! How did you determine which ones to replace?
    How did you go about replacing the modules? Did you pair the modules by capacity and balance the whole pack? A bit naively, it sounds like perhaps one of the modules is badly paired or over/under performing so when it charges/discharges significantly (on long drives) the voltage drifts beyond the acceptable threshold.
    I have only worked on my own battery, professionals have significantly more sophisticated equipment although as I understand it the process doesn’t differ too much, just waaaaay faster and more consistent. Googling quickly it looks like there is a place near you that provides exactly that service: https://www.ericsautohamilton.ca/hybrid-repair-and-service – have you reached out to them?

  3. Cellia

    Great site and info!! Glad I left YouTube and found your site. I plan to do this by my self (no experience, but determined). I need to save $$ and get my battery/car to last another 2 – 3 years. I just need to confirm a couple of things. Are steps 13 – 17 really necessary? I don’t have that kind of time or space. BTW who helped you get it out of the car…it looks really heavy. I am not that strong. PLUS it looks VERY time consuming and intimidating. I have seen it done on YouTube https://youtu.be/R0OrRPT2EsM without charging the modules and using an app to check each module voltage with a scanner or app. (Dr. Prius). I can purchase the meter thing and possibly wait the 6 hours to have them balance (that looks really simple and you only used 2 copper wires..REALLY smart and cool). This person https://youtu.be/irddAVZaJb4 did not balance them or charge them and he said he got another 10k – 15K out of the battery before other modules started to fail. Last… can I balance them on a later date (like a month later) after replacing them?
    Looking forward to your reply… I know its been a while since you put this up, but so far no one is replying to my questions.

    1. tobymurray Post author

      I wrote this all a while ago, but just in case I didn’t cover it: ensure you’re being safe, and don’t do anything with the high voltage stuff unless someone else is around. Electricity is simultaneously not as dangerous as people think and much more dangerous – if you don’t know what’s going on it’s really hard to assess the level of risk and when something goes wrong it goes wrong FAST.

      Massive caveat to the answers below, what I read to support doing this myself is almost all of my electrical knowledge. I have no formal education around electrical engineering, so it’s possible I could be completely wrong.

      > Are steps 13 – 17 really necessary?
      Evaluating the capacity of the modules is not really necessary, no. By skipping that step you potentially miss a dying module (necessitating doing the whole thing again in the future) and you miss out on the opportunity to reorder the module so they’re matched up.

      Additionally, charge cycling the batteries is a way to increase their effective capacity, giving you overall healthier cells. The batteries have a “memory” and dropping them well below where they usually would and then charging them to above where they usually would “resets” their memory.

      If it’s been a short time that the Prius has been out of commission, you might be able to get away with not balancing the modules, assuming you charge any new ones to exactly what the other modules are. If they’re not aligned, you’ll have no real choice – you could theoretically selectively charge/discharge modules but I think it’s altogether easier to balance the pack.

      While I have no experience with them, I’ve seen whole-battery chargers. E.g. they put out 200 VDC (or whatever is needed), so you discharge the entire battery completely then charge it up all at once, then repeat 2 more times. I think when I looked they were a couple hundred dollars, but well worth it if it works! That would be much easier than what I did, I imagine.

      > who helped you get it out of the car
      I got it out of the car (and down the stairs…) myself, but I’m a bigger guy – I’d definitely recommend a second pair of hands if possible. In addition, wear thick clothes and some gloves because it’s just sheet metal and the edges can be pretty sharp if it slips at all.

      > did not balance them or charge them and he said he got another 10k – 15K out of the battery before other modules started to fail
      That like what I’d expect- from my understanding the Prius’ charger is not designed to rebalance a pack, it relies on roughly matched modules charging and discharging as a team. Maybe modern EVs have more advanced systems that can accommodate things like that?

      > can I balance them on a later date (like a month later) after replacing them?
      If all the modules in the pack are not within some threshold (+/- 0.15V or something?) then the car just won’t start, regardless of the cell health. If you put a new module in with a bunch of old modules and don’t rebalance it, energy will be disproportionately drawn from the stronger cells. My understanding is that this can significantly impact the life of the cell, although that might mean just bringing it in line with your other ones?


    I know it’s 5 years later but, thanks for the excellent blog articles. I’m Prius shopping and looking at Gen 2s because I’m cheap. Great info I can use as a DIYer if needed.

    1. tobymurray Post author

      I’ve seen recently that there are a bunch of “whole battery” chargers that are accessible at a consumer price point. I have no personal experience, but it seems like (barring bad cells) you could refresh an old battery without taking the battery out. It’d save like 98% of the work if you could cycle the battery in place, so might be worth considering including that (a few hundred dollars?) in the purchase price of an old Prius.


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