Been riding dynohubs for 14 years. The one that old (SON) has never been serviced for bearings. It still runs nicely. Notchiness when spun by hand is normal. The speed that you can spin the wheel on the bike by hand is quite a bit slower than the speed the wheel will spin when you ride it.

Ride and enjoy the freedom of not having to worry about battery life... ever.

And yes, it is best to have the hub bearings serviced by someone who knows how to do it. Much has to do with the insulator's fragility and, IIRC, the direction it undoes, along with the tiny wires involved. Not even I have been game to fiddle with that aspect.

If my original dynohub does finally cease to operate efficiently, I might give it a go... it has done around 50,000km and certainly paid for itself time and again.