I personally bought a 12v generator off "Wonderfull Creations" .
If you have a China Girl it fits nicely into the exsisting set up with not much work needed.
I then bought the charging unit/rectifier of "Wonderfull Creations" and have been running a 12v SLA for over 18 months with no problems at all.
I have x2 12v MR16 4.5 watts led front lights and an led stop/tail light with front/rear indicators.
If there is no juice in the battery the lights will still run as long as the engine is ticking over, albeit not as bright as a full battery.
The plus side of having a battery is you still have lights when the engine is dead!
The cost is well worth it espeacially as it works!!
I have filled up at petrol/Gas stations and just carried some 2 stroke oil in my bag to mix in with it, albeit the exact ratio may be slightly out but better being on the cautious side than seizing your engine!!
Happy Biking, Pete.