are you having problems? a generator won't charge much, if at all, at idle, but under normal conditions the discharge from starting should be made up pretty quick once you get above idle, particularly driving it - there's not really a "formula" because time depends on the state of charge of the battery

Bill


Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics