"Do you power the glow plug all the time, or just for starting and then engine continues to run with battery disconnected? "

you still haven't absorbed the method by which a glow plug works in a glow-engine! .... there is a catalytic reaction between the methanol and the platinum in the element which keeps it hot..... no methanol, no catalytic reaction.... gas only or very low methanol content will require a battery to keep the plug lit....

[:-]