If the battery sits for two or three weeks it will self discharge on its own. You should check the batteries periodically to make the sure the voltage doesn't drop below 3.2v. If the voltage is around that I would but it on the charger for little bit. Keep in mind if you overcharging and discharging below the recommended voltage for a one cell lipo that will decrease the performance and life of the battery.

As for your stock charger I would assume it has a shut off once it hits the full voltage, I would check the manual to be on the safe side.

Also temperature will affect the lipo greatly. Do not leave a lipo battery in the car for any length of time.