Yes, the light located on the charging brick will change from red to green when the board is fully charged and will stop charging automatically. Leaving it plugged into the charger will not cause any long term damage.
The Onewheel battery is made up of many cells that work together to hold a charge. Sometimes, a few battery cells can get out of balance with the other cells and don’t get a full charge, causing decreased capacity and therefore decreased range.
Fortunately, the Onewheel charger continues to “balance” the cells after the light has turned green. However, this is a very slow process and can take up to 72 hours in some extreme cases. Fortunately, this is rare, but this is why it’s a good idea to give your battery a occasional overnight charge or just leave it plugged it.