I haven't had any battery issues...usually, my Rovio will last right at 3 hours off the dock while streaming 640x480 at the highest quality. (That's not 3 hours of driving, it's about 0.1 hours of driving and 2.9 hours of sitting in one spot streaming video...I get bored too easily to try to keep driving the thing for long periods.) I do think there's a firmware problem where the charger stops charging too soon though; within minutes of driving off the dock, the charge is only showing 80%. If I undock & redock after it has finished charging then that doesn't happen and it'll usually run for 3.5 hours on the next outing. Perhaps they're trying to preserve battery life by making sure they don't overcharge or something.
I have had an issue sometimes where within about three minutes of leaving the dock the unit stops streaming video and is completely unresponsive (the open browser just shows a black screen, and after closing that browser I can't connect to it with any browser or RovioDirect) until I physically power it off and then power it back on. During this non-responsive period, however, it is still responding to pings. It's like the web server has crashed, but the unit is still functional. This is with firmware v5.03. Each time this has happened it's been connected via IE8, it's never happened with Firefox or RovioDirect. That could be a coincidence, or it could just be random luck.
Has anybody else seen this issue? I've seen a lot of other issues reported here, but not this one.