I have the charging rate of my generator set to about 14 amps, it works out to 1 amp + charge with the lights on( Quartz Halogen), the Optima battery is now about 14 years old, about 7 years ago it was on the trickle charger for 10 min because I left the ignition on for 3 months ---hand cranked it, drove it for 60 miles without turning the lights on ----normally I turn on the headlights after about 40 miles, turn them off about 10 miles from home if it's daylight, the generator has been more reliable than the alternator in my 74 chevy truck(same type as used to make A alternators)---it has been rebuilt 3 times in the same miles over 30 years ---I havn't touched the generator except to adjust the charge in 40 years.
It says in the owners manual that the ammeter should show a discharge with the headlights on.
With a generator the belt should seem to be quite loose ---it doesn't need a lot of tension to prevent slippage at the generator ---with the small pulley the alternator needs to spin fast the belt needs to be tight to prevent slippage ---them you have to think about water pump modifications, belt wear