It’s possible to get a pretty good deal on used Toyota Prius cars, but as with all hybrid cars that also means a used battery pack and resulting issues. In the case of the Gen 2 Prius that [HubNut] recently acquired it was clear that its battery was effectively toast, with the engine running constantly and the car often giving up due to detected issues with the pack. After getting to an EV-focused garage for repairs, a spare NiMH module was used to replace a problematic module to bring it back to good health, while raising the question of how sensible such a repair is.

Certainly, compared to the average BEV where a much larger battery is generally integrated well into the frame, a Prius makes things very easy, with the compact battery readily accessible and removable from the trunk. It is also a very modular battery, with some elbow grease and bolt-twisting enough to disassemble it.

Even with that it still a high-voltage battery with all the associated risks, and as raised in the comments there’s a big question about putting a new(er) cell into a pack with more worn-out NiMH cells as generally the cells wear out fairly evenly. While this fix can give the pack some more life, the new cell won’t match the internal resistance and other parameters of the pack, leading to issues like voltage drift. Then there’s the issue that if one cell failed, others probably aren’t far behind, so this hack would soon become a regular ritual.

Much like swapping one bad 18650 Li-ion cell in a bigger battery, it’s probably a more sustainable solution to simply replace the entire battery at once, or at least replace all modules or cells to properly refurbish it. For [HubNut] this fix suffices because he suspects that this pack was already assembled from random modules, it’s an important consideration to make if you don’t enjoy ending up stranded during a trip.