I wish I had a dynamo light instead of the Nightrider light I paid $120 for. Maintaining the battery is just too complicated.
If the battery just needs to be "topped off" (how do you know??) you charge for 4 hours. That means I'd have to charge it as soon as I get home and stay up until at least 10pm (I go to bed early) so I can be sure to unplug it in time. Don't forget!
If the battery is exhausted (which you aren't supposed to do), charge it for 9 hours. The only way I can do that without setting an alarm clock for the middle of the night is to charge it at work. That I don't mind, but what if the battery isn't exhausted yet, but there's not enough power to get home? There's nothing to indicate this.
Dynamo sounds perfect. No babysitting batteries.