I'll add my experience with a hybrid battery pack failure at nearly 94,000 miles, starting with user error (i.e. me). About 3.5 years after the purchase of my 2000 Insight 5-speed, the original 12-volt battery went dead on a couple of weekends. The hybrid battery gauge was at zero - the radio lost it's stations.
I just put the battery charger on a couple of times when this happened and got a replacement 12-volt battery.
This was probably the worst thing to alllow happen to the hybrid battery pack.
An old cordless phone of mine was notorious for needing a battery replacement if the charger was disconnected for a few hours. It may not have used NiMH batteries, but totally dead batteries must be bad in the Insight as the BCM and MCM units apparently protect against that.
The second worst thing is keeping the Assist on for over thirty seconds at a time - let off on the accelerator and/or downshift.
I did not do much hypermiling the first three years of my Insight. In fact, it was on the fast side (70-75mph). At least three evenings a week, someone would get me hissed off, and I'd pick up the gauntlet, doing 95mph typically. This would obviously stress the batteries. This was on the Bush Tollway before the state troopers and higher gas prices pushed the speed limit under 75mph (in a 60 zone). Failure to drive on the rightmost side also inadvertantly made it easier for the aggressive drivers to get under my skin. On an out of town trip, pride did it again when I cruised at 95mph for about an hour and a half to keep a @#$# Suburban in my rearview mirror in the Texas panhandle. Yes, I put a strain on the Assist.
I think it can be said it's remarkable that my Insight went over 93,000 miles with only an O2 sensor adjustment....
It's come up in forums before - do battery packs in manual transmissions fail faster than the ones in automatics? My answer is: "
No, unless you drive it hard". If the 5-speed driver remembers to downshift more during climbs, watch the charge, etc, the battery pack life should be just as long as a hybrid with an automatic. I'd go so far as to add be even more careful if you buy the MIMA hack for the Insight - you don't want the charge to dip under 40% and shorten the battery pack life.
The software in the MCM and BCM units are supposed to be improved, so I expect with better hardware and better driving sense, I could go at least 150,000 miles on this set of batteries.