I have left mine for well over a month not plugged in without any issues. Hadn't thought about using a battery tender. Like others have suggested you could just leave it plugged in, even if on 120v. Not sure if it is good practice or not, but when leaving it parked for a long time and plugged in, I usually charge to 80% but then set the charge limit to 50% and let it slowly discharge over the month or so.