I've ended up having to explain the difference between Li-ion and NiMh batteries to people a bunch of times, and why lithium batteries often seem to have a longer service life, and have started to describe the general situation as "The penalty for a poor charge controller design with NiMh is the battery doesn't work for as long, but for lithium ion the penalty is that the battery catches on fire. So more design effort goes into lithium battery chargers". This is independent of other differences in the tech, such as power density. NiMh can last a long time with a good charge controller.
However, for cars it seems like the need for marketing to push range numbers as far as possible led to compromising the safety envelope. I've got two first-gen Honda Insights (2000 and 2002), which of course was a battery-assist hybrid with a small NiMh pack in the back. The OEM charge controller does a poor job of managing the pack, they often end up unbalanced, and most cars had the pack replaced once under warranty at about 10 years of service. The DIY community of course stepped in and produced aftermarket plug-in chargers that we wire to the pack to trickle charge- individual cell status isn't managed since you're just wired to the whole pack- the strategy is to just trickle charge it until the whole battery voltage gets to a certain level, which means some cells in good shape are still being charged that whole time and that excess energy gets dumped to heat. But of course unlike with LiIon, they don't catch on fire ;). Of course all-electrics have batteries much larger than the original Insight, and require the power density of LiIon. It's just an interesting contrast between the battery types with respect to battery management strategies.
However, for cars it seems like the need for marketing to push range numbers as far as possible led to compromising the safety envelope. I've got two first-gen Honda Insights (2000 and 2002), which of course was a battery-assist hybrid with a small NiMh pack in the back. The OEM charge controller does a poor job of managing the pack, they often end up unbalanced, and most cars had the pack replaced once under warranty at about 10 years of service. The DIY community of course stepped in and produced aftermarket plug-in chargers that we wire to the pack to trickle charge- individual cell status isn't managed since you're just wired to the whole pack- the strategy is to just trickle charge it until the whole battery voltage gets to a certain level, which means some cells in good shape are still being charged that whole time and that excess energy gets dumped to heat. But of course unlike with LiIon, they don't catch on fire ;). Of course all-electrics have batteries much larger than the original Insight, and require the power density of LiIon. It's just an interesting contrast between the battery types with respect to battery management strategies.