I haven't had any unusual problems with either battery. The one that's part of the hybrid system (with the charge shown on the display) is managed by the car. It just runs on 100% gas engine if it's low.

The other battery, which is like the one every car has, died on me last May. But I think I left the lights on in the car, and it was a couple of days before I used it again so they were on for a while in very hot weather. It was easy enough to recharge.

There are something like 16 different computers in the car that are maintained by the battery while the ignition is off. But they're not related to they hybrid transmission -- they work things like the lights and smart key. I assume more and more cars will have that many computers as time goes on.

The thing I like least is probably the gas tank. It's a flexible bladder (part of a design to prevent gas fumes from escaping while you're filling the tank). In cold temps the bladder is less flexible so it doesn't take as many gallons when you fill it up. This hasn't caused any real problems for me, because gas stations are common enough around here, but it makes it hard to estimate how far you can go on a tank of gas.

Also the gas gauge is not linear. It's 10 LCD rectangles on the dashboard, but each one does not represent 1/10 of the tank. In the summer I might go 100 miles before the first pip disappears, but in winter it's more like 30-50 miles. And you don't really know how much gas is left when you're down to one pip.

But I would still buy another Prius in a heartbeat.