"overcharging" doesn't exist. There are two circuits preventing the battery from being charged beyond 100%: the usual battery controller, and normally another protection circuit in the battery cell. Sitting at 100% and being warm all the time is enough for a significant hit on the cell's longetivity though. An easy measure that is possible on many laptops (like thinkpads) is to set a threshold where to stop charging at. Ideal for longetivity is around 60%. Also ensure good cooling.
Sorry for being pedantic, but as an electricial engineer it annoys me that there's more wrong information about li-po/-ion batteries, chargers and even usb wall warts and usb power delivery than there's correct information.