Should I leave the MH plug in all winter?

I plug mine in for 2 weeks then un plug it. Makes starting the genny easier for the monthly exercise

I leave the batteries in the 5er, have a Progressive Dynamics charger, and plug into a timer so that it runs for 3-4 hours each afternoon. Worked great last year, batteries continue to be in good shape.

I keep mine plugged in all year. That way I can run a heater in it and not have to put antifreeze in. I can also in a moment get it ready for a trip. I check my battery and charger weekly.

If you have a smart converter yes, if not then no.