Looking at used Prius. Concerned about battery. Am I understanding how to recondition correctly?

Sooo, @ more senior members - correct me if I'm wrong.

If you go down the rebuild route, make sure that you research what the rebuilder does. Even then, a grid charge once every 6 months looks like good preventative maintenance.

Look up @2ktoaster's new batteries - looking pretty solid. Disadvantages IMO are 1) no long-term longevity proof (long-term as in 10 years, no reported issues thus far), 2) can't replace individual modules with regular prius ones if you have trouble. Dealer batteries are a bit more expensive, but there's no question what you're getting. CEBA batteries don't look like a good idea at all from what I've read.

1. There's torque, there's techsteam (get it, just get it, it's useful for so many things it's ridiculous), and there's "hybrid assistant" (HA). For hybrid assistant you'll need a nice OBDII bluetooth VIM ($80 approx). It has a semi-automated high voltage battery test that can give you a decent idea about the state of health of the battery. It basically graphs the modules' voltage rise and decline over an in-car battery drain and force charge. At-rest module voltage won't tell you much unless a cell has shorted out - then it's ~1.2v lower than the rest. If the car throws a code (P0A80) but all modules look fine, it should store freeze frame data for the error that you can retrieve via techstream. It'll list all monitored values at the time of the error being set - that's how I know that module 15 or 16 (or possibly both) are failing on my battery (gs450h, only during wide open throttle acceleration at unreasonably high speeds, and only every now and then... or if I floor it at a low state of charge or try to drain it in EV 'till the end - then it logs a pending and is fine on next powerup) - the car logs ~-1.2v lower on a particular pair of modules. At rest voltages are fine, so that probably means that a cell within a module has very low capacity compared to the others. Only way of fixing the module that I know of is rehydration - assuming the module is structurally sound (hasn't leaked). There's a thread about it here.

2. It's best if you find modules similar in capacity and internal resistance. This means measuring all your modules somehow... which means pulling the battery apart. By the time your battery throws a code (pending or otherwise), all your modules are usually in a varying state of health. The ones in the middle of the pack are usually worse off than the rest due to heat build-up, but the variances can be all over the place. A pro rebuilder should have a nice stock of modules to make a matching set of 28.
My guess here is that if you have a module or two way below capacity, they will fail very fast as the car is cycling them across a larger capacity span than the others. At any rate, from what I've read it seems like cycling all the modules (the replacement(s) and the others) a few times down to whatever voltage you're not scared of (with interim balancing overchargers) and then balancing the pack is the DIY way to go... and then hope for the best.

3a. You will balance the cells in each individual module, but the modules won't be balanced together. You'll need to charge the battery as a whole for that. Now if you're talking about cycling, cycling individual modules seems better than using a whole-battery discharger - you're dealing with 6 cells at a time instead of 28*6.

3b. Prolong's system, DIY using LED drivers or whatever, plenty of ways. I went with Prolong's charger + intel discharger. There are guides on how to build your own grid charger for honda IMA batteries - if you understand them, you should be able to understand how to build your own for the target voltage. Prolong's charger adjusts charging rates according to battery SoC (and probably does other things better too) so the simple DIY charger isn't just cheaper in cost... well depends on what simple means I guess

Soooo, to sum up:

1) Get techstream and hybrid assistant - this means techstream-compatible VIM, and an HA-compatible VIM. Not necessary but both are very helpful. I'd get techstream first, as you can plot the HA data yourself with it (or with torque, for that matter).
2) If you get a code but at-rest voltages are similar - check the freeze frame data for the code with techstream. You should have an outlier with low voltage there. Cycling the modules at that point might restore the pack to usable condition - anything from near-brand new to near-failing, probably with a bias to the better outcome.
3) Buying rebuilds/refurbs doesn't seem to be recommended around here, high rate of failures. If you can get somebody to do the proper things, consider the price and go ahead. A new battery from Toyota is probably the best bet, 2ktoaster's packs seem to be as good (and so far proven to be the same, performance-wise, longevity unknown due to age of deployments), and a bit cheaper. Look up the prices and decide. Main differences - module format, can't mix and match.
4) If you're rebuilding - cycle your modules multiple times to recover lost capacity, balance the pack as a whole as otherwise modules can drift out of balance (unless you can balance all of them at about the same time ^_^). Matching modules to make a pack is preferable, but usually unfeasible for a DIY repair.
5) Maintain using periodic balancing (say twice a year). Not sure about cycling maintenance frequency.

Bah, I hope I'm not forgetting anything.

 

The short answer is just to save money toward a new Toyota battery pack. That is the most proven method to get another 10+ years out of a battery. Prolong seems to add time but 10 years? If you can install it yourself it’s not as expensive as it seems. When your battery finally does go you just sell the used system here and recoup over 50% of the original price.

Have you thought about buying a Prius with a bad battery pack going in and just replacing it with a new one? You can find dealers that will sell you one for under 2000 and most people cant replace them themselves. Might be a little over 4000 total but you would have a battery that would go at least another 10 years.

 

Joe,

Find yourself a decent Gen 2 that has a failed battery. Then look me up. I wouldn't be all that concerned about trying to find one with a certain mileage as I would be about finding one with a good body, good interior and some maintenance history. Deals are out there, sometimes it just takes a bit of patience. You should be able to get a good one for 1k-1.5k max.

 

Orrr... Skip it and spend less money for a much lower mile, or much newer, Corolla, Fit, Matrix, Civic, Etc.

No worries about replacing a hybrid battery ever.

This is coming from a guy who fixes Prius for a living.

But if you decide to roll the dice on a used Prius....
In additoon to the other great info others have provided, since you are $$ conscious, why not build your own whole-pack charger? Cost you under $100.

If you are really cheap you can skip balancing the pack. Just make sure the random module throw in is at least close in voltage to the existing ones.

You may have to go in there quarterly (maybeore often?) to swap in a module or fuss with things, and it won't be reliable, but it will be cheap. Really cheao, so maybe it is worth it? Only you can decide.Keep messing with it as long as it is fun for you.

Feel free to call if you want to chat about your ideas.

 

How do you build a whole pack charger?

 

I like skibob's suggestion best. Find one where the traction pack is known to be failing and also proven to be the only significant problem on the car.

Get that car cheap, put a brand new Toyota pack in it and enjoy it for 10 years.