1 of 28 is Bad Gen 2 (2007) Battery Module. Can I put in a single Gen3?

You can, but resting voltage can lie to you. I've seen a few show good voltage with no load and fall on their face under a load. Also, you're not improving the capacity of any of them unless you recondition them. Kind of like playing whack-a-mole. It will work until the next one fails.

 

Sorry but as mentioned above resting voltage really tells you nothing about the module. You must load test them at a minimum and cycle them too if you want to find out their current capacity (for matching in the pack). That is really the only way you can rebuild the pack and have it work for any length of time reliably. Some may get lucky but far more ending up wasting alot of time doing the same work over and over. Contact "ericbecky" on here if you need good 2nd gen modules.

 

To properly load test them, you should use something that can give it enough current to somewhat replicate what the car throws at it. I find the method of using a 55w car light bulb is equivalent to a fart in a hurricane. Won't catch the bad ones

When you say you can't find a gen2 module as good as the original 27, did you mean the voltage reading? Not sure how you came to that conclusion

 

Short answer: No - the internal resistance of the gen 3 modules is lower than gen 2 modules. If you use it, it will come out of balance with the other cells in the pack for this reason. I highly doubt this will work more than a thousand miles before throwing a code.

Search PriusChat for the proper technique to refurbish battery packs. There is a lot more to the health of modules than just resting voltage. Quick summary: The generally accepted method is to do a 3x charge-discharge cycle on each module to restore capacity, tracking Ah capacity for each module. Then a load test is performed. Poor performing modules are replaced. Finally all modules are balanced with each other (not just voltage!).

 

I have plenty of Gen 2 modules if you need them.

In my opinion I would buy them in pairs from the same pack, knowing that you will likely replace another in the future.
This will help diminish some of the variability.

You can put a gen 3 in, but then, besides the usual amount of variables, you've added in even more.
Unlikely the car will tolerate it very long... but who knows. Are you feeling lucky?

If you have a charger/discharger, you might be able to hammer on the pack and mask the variability by running a few cycles once in a while.
But is it worth it? Only you can decide.

 

even the long cuts are iffy.

 

The only sure thing are hair cuts.

 

unless you're bald, then the term, 'a little of the top' can be frightening.

 

I'm not looking forward to that reality .

 

The car headlight technique does work as long as you use both the high and low beams together for exactly 2 minutes per module, see here.

Gen II Prius Individual Battery Module Replacement | Page 13 | PriusChat

The battery module passed all other tests including capacity and resting voltage over time but failed under load (that's how I found it).

 

For the most part that light bulb test will work. However the modules that would fail when the voltage is low, this test may not catch them.

I use a 60A load tester when I have a questionable module. That type of current will catch the bad ones when the voltage drops......in about 15 seconds

 

I totally agree the larger the load the more you will separate the good modules from the bad (larger loads up to 100A are closer to actual service). From what I've seen loads over 100w (single headlight is not enough, need both low and high beams hooked up, H4 bulb works well) for 2-3 minutes will usually allow you to see 99.9% of the bad ones quite easily. Testing method assumes exact same load and time tested on each module. The larger (60A) load you use may also help to match the modules (voltage drops) to each other better, haven't experimented with larger loads enough to know how much difference you might see as a result. I would just caution anyone to be very careful when using loads close to actual service (100A max) to ensure you stay within the 40-80% voltage range (hyper-cycling) on the modules so you don't lose any battery life in the process. I typically suggest the headlight method for most simply because it works well in the vast majority of cases and is definitely less risky if you are still learning the rebuild process.

 

Additionally, consistency is key.
Whatever method you choose, be consistent so you can compare results.