My 2004 Prius still has its original NiMH battery. I
restrapped it in
2016, and do keep an eye on its particulars. It seems to still be
generally fine; maybe a little capacity loss but it can still absorb
400 vertical feet of elevation coming down a mountain road before
hitting the "full" mark at 80% SOC. Now that I've got the Kona and
am driving the Prius less, I've noticed a little imbalance and weirdness
after it [ the Prius] has been sitting for a while, but that has so far
seemed to straighten itself back out after a bit of driving. Without
any obvious "recalibration" cycles, too. I have a couple of spare "good"
modules on deck of roughly the same vintage if it comes down to
playing the whack-a-mole game sometime, but in New England the
car might become a hopeless pile of rust before then. It's had a *very*
good life, and ain't dead yet!
We have to remember that hybrid packs get socked with pretty obscene
charging currents during regen, too, like 100A == *15C* rate into the Prius
pack. That NiMH chemistry just sucks it right up happily, at least for
those short bursts. Big EV packs generally don't have to deal with that
level of abuse, and most of them probably couldn't even in optimal temps.
_H*