It is hard on the battery to recharge it with the scooter. The charge rate is too high for too long
and the battery may overheat. Overheating can cause the electrolyte to boil away
and it can warp the plates in the battery. A battery is made of metalic plates separated by insulator plates.
Warped plates can short, thus ruining the battery.
It is best to slow charge a battery with a battery charger at no more than 10% of it's capacity....
For example, a 10 Amp-Hr battery should be charged at no more than 1 amp/hr,
which is what a typical trickle charger puts out. A 10 Amp-Hr battery is typical of many scooters and small motorcycles.
So, it would take about 10 hrs to fully charge a fully discharged battery.
It is best to own and use a charger/maintainer which reduces the output voltage when the battery is charged.
When you ride infrequently, like winter, using the maintainer to keep your battery fully charged is a good idea.
We connect a maintainer about every 2 weeks when we don't ride. Our batteries are relatively new and don't
lose much capacity over a 2-3 week period. Old batteries may need a full-time maintainer.
You need to see if your battery uses a liquid electrolyte and if it is low. If low, add distilled water ONLY.
and then charge the battery.
You can buy a Schumacher battery maintainer at Wal Mart for about $20
and Sears often has a similar one on sale for about the same price.
Now back to your question. IF you have a 10 Amp-Hr battery and your scooter has a 30 Amp eletrical generation system,
it probably uses 10 amp for running the engine and lights, so that leaves 20 amp to charge on your battery.
That is about 1/2 hr if you are running the engine at moderate RPMs. Yes, the electrical generation ususally is higher at
moderate RPMs than at idle, which is why the lights get brighter when you rev the engine.
Gosh, I always wanted to be a teacher.. I hope I didn't bore you.
Scoot Safely,