With out of warranty replacement battery pack costs being reported in the $4,000 range at dealer prices, I am wondering if DIY packs would be a realistic option for handy people who have a decent soldering iron and aren't afraid to use it.

With C cell prices on NiCad @ $2 ea and NiMh @ $3.50 the cost for replacing a bad battery pack would be no more than about $500 and a few hours of your time. Quite a savings!

I have built a replacement pack for my bicycle lighting system, which was quite simple, WAY cheaper than OEM replacement, and which works as well (or even better) than the original battery. Why couldn't the same thing be done on a spent HCH battery pack?

Assuming the size and capacity of the replacement cells were the same specifications as original, there should be absolutely no problem with compatibility of the HCH charging system. Heck, it might even be possible to use a higher capacity cell, if the recalibration program has enough latitude built into its programming.

So, I'd be very interested to hear back from those of you with some detailed knowledge of the system and battery specifications about whether or not you think the project could be a reasonable option for those of us unwilling or unable to cough up four grand to keep their aging hybrids on the road.

There are a couple of issues you'll run into:

1/ The batteries used in the HCH pack are designed for extremely high input/output currents, much more than regular D-cell NiMH batteries, I believe they do this by having very thick electrodes the trade off being that they have a lower mAH per cell (check the specs and you'll notice this). If your replacement cells have higher mAH capacity but lower current limits the pack would have more actual power capacity but a shorter lifespan.

2/ The cells have some kind of custom thread things on the end that allow them to screw together, creating very robust low resistance connections between the cells. If these are spot welded on the ends I guess it might be possible to grind them off and re-spot weld them on the new cells.

These issues aren't impossible to overcome and as more and more hybrids are on the road the market will open up to specialist companies who will re-condition old battery packs, testing and removing the bad cells and replacing them accordingly. I reckon with refurbs like this an average pack would probably last 15 years before it would be completely dead which isn't bad. In that time frame the game will have moved on completely with new cars/batteries/technology making our current hybrids out of date.

I agree that NiMH may be history as Lithium Ion cells are made available for use in cars. I believe, today, manufacturers are still afraid that the Lithium Ion Batteries could explode.

Li-Ion costs more than NiMH and they have stricter charging requirements. That's why there were exploding laptops due to faulty charging. The Li-Ion can rupture from a over hot cell.

One thing that I've read about the expense of these batteries is that they have to all have a very similar charge/discharge profile. This makes sense because if you have half of your cells discharging at one rate and the other half at a slower rate, the discharge/charge is going to happen a whole lot more on the faster batteries. This will shorten their lifespan.

When you're buying off the shelf and sticking two AAs into your digital camera, it doesn't matter if one battery is discharging ~10% faster than the other. When you daisy chain a couple hundred D cells together and are motivating a 3,000+ pound car, this would matter.

My thoughts are that hybrids will be like iPods. When my iPod battery finally dies, I won't get an Apple OEM--I will buy a 3rd party battery with twice the capacity at half the price. If battery failure ever becomes an issue in these cars, there will be lots of companies stepping up to build replacements. That being said, I highly doubt that I will replace either of my hybrids' batteries because of failure--it will because someone comes up with a great Li-ion aftermarket option with more juice and less size.

Commuter car, grocery getter, and summer road tripper--average 10k miles per year.


Winter road trips and ski trips, bad weather commuter and my wife's "daily" driver--expected average 4k miles per year.

Assuming just a few of the cells go bad, are individual cells available for purchase at this time?

The HV batteries from Toyota, Honda and Ford are single field replacement units.
You would need to go outside official channels to rebuild a battery pack. I have
seen instances of people repairing Prius and Highlander battery packs, but they're
"professionals" or advanced enthusiasts.

cheers,
Bill

I'm a ridiculously active enthusiast. Does that qualify me?

Seriously though, thanks for that info and welcome to GH.

Hi giantquesadilla,

Thanks for the welcome.

Regarding the battery packs, you do need to know what you're
doing. The HV safeties are no longer in place when you're into
the pack. Some knowledge, good sense, and cat 0 insulating
gloves and 1000V rated meter would be required at a minimum.

cheers,
Bill