Both to some extent but sitting idle, either on the charger or off, is
tough on batteries (particularly Ni-Cads). That is why cordless drills
get such a bad rep from homeowners and contractors seem to be fine
with them.
Yes, I buy all corded tools for just that reason...infrequent use.
Our handyman is always going from one battery to another.. using my electricity to charge the dead one. I may have to start charging him. ;-)
That can sure get expensive. Make sure you give your handyman change
for a dollar.