I am always looking at having a backup plan, and in the meantime of rebuilding my Hybrid battery pack, I am curious if age or mileage is more degrading to a hybrid module. If say 10 modules end up needing replaced, the cheapest I can seem to find them on eBay is $30 shipped, so with tax and all, I'd be looking at about $321 Looking on some junk yard websites, there are a few 2012-2015 Prii with under 100k miles that have the hybrid packs for $500-$600. Would a 2015 Hybrid Pack with 100k miles most likely have all good modules, and if the car has sat like a year, would that have a very negative effect on them?
Yes, the newer the better. Sitting for a while only would be a problem if any of the modules were defective. Even if any of modules self discharged to zero volts, You could safely charge it back up as long as it was defect free. The secret is to use a very low 0.05C charge current until it reached 7.2 V. This is in fact true for any module that was less than 7.2 V. Unfortunately for you, the only way to know whether you got a bargain or dud is to take the risk and then test them. The newer the pack the lower the risk - all things being equal.
Everything stated above is true; but you missed a couple of parameters. Heat; if the wrecked pack is from a car that was driven in the southern desert states; you'll more than likely to find more dead/defective cells. Impact damage; even if the battery case is intact - there's a good chance you'll have many more dead/defective cells. IMHO: buying used and properly tested batteries from a reputable dealer would be the safest option. Purchasing a used pack; yields you a back-up pack that you can slowly reassemble and do a quick swap-out; should your pack fail again. If you decide to go this route; you'll need a few battery charger/testers to go through each individual cell. The last time I checked; they ran several hundred to several thousands of dollars. Hope this helps......
3rd gen battery quality rebuilt from 2nd life Toyota Prius Hybrid Battery Refurbished Balanced 28 Module Set 10-15 3 yr Warr. | eBay 2016 Prius Nimh pack in Des Moines IA, 39,000 miles $650, Sam's doesn't ship, probably why its been there for 2 years.