Depends. Some older style chargers will over charge the battery, boiling all the water out.
What I have done in the past (if I have an older charger) is use a 20A timer on RV, and only turn power on for a couple hours per day.
Some chargers (most modern) have multi charge stages and its OK to leave them plugged in all the time.
But leaving it plugged in comes with a price. Last winter I left my RV sit on property my Brother and I own. I don't know the price per HW hour, but my RV was the only thing on the circuit last winter and the bill went up $20.00 per month.
