Two for two in 12 months

poor luck, most likely. the only way to get solid performance is new, unless you personally knew the history of the used battery.

 

1. HV batteries will last about 10 years, so if you put in a 3rd pack from a 2004-2007, it should fail again and you'll have more disappointment
2. You can watch youtube videos and it will give you a general idea of how to disassemble a pack.
3. If you want to invest in reconditioning equipment, Hybrid Automotive sells a kit for about $750.
4. You would clean the bus bars of all the corrosion and then recondition your battery using the kit.

It's easier than it sounds, but it's not too difficult.

Or if you want to do a band aid repair, just disassemble the pack and pick out all the bad modules and replace with the good ones you have available.

 

without doing it proper which is very time-intensive and you need Chargers seems the easiest thing would be to to drain both packs and let them sit overnight then pull the obvious bad cells and toss them, now take the other cells that you think are good and make an average voltage and write that down now try & get enough cells that are very close to that average voltage to make a new battery and you're good!

If you try and only keep the very best cells not only will you not have enough to make a battery but you will be more likely to damage the week cells because they will never reach charge because the good ones will get there first causing the bad ones to over heat or will just simply ever reach pair to the good ones, that's the poor man's way of doing it I would think but my disclaimer I've never done it before but I do know a bit about batteries.

In a nutshell the weak cells tend to pull the good cells down to their level, so if the final pack or product cannot reach nominal charged voltage the whole pack will tend to overheat as it tries to accomplish that impossible feat