I think that's a key issue. Batteries just can't be trusted over time. Properly cared for they decline at a sort of predictable rate but drain them too much and all bets are off. At least with an 18 gallon gas tank you basically know how far you'll go today, tomorrow and 5 years from now.
Well the thing that’s really pissed off a lot of leaf owners is that they are used to recharging rechargeable batteries fully. Apparently if you keep doing that with the leaf, you quickly start reducing the batteries’ capacity. I didn’t think Li-on batteries developed “memory” issues like other rechargeables but apparently this is an issue, at least with the leaf’s batteries and charging method. They say not to fully charge it every time you’re done driving.