We have a battery-powered drill that my girlfriend brought with her when we moved in together over 7 years ago. We use it very rarely, probably once every 4 mon

We have a battery-powered drill that my girlfriend brought with her when we moved in together over 7 years ago. We use it very rarely, probably once every 4 months. We don't even have a charger, and the battery has never been changed. Still enough charge to screw into particleboard. I hope someone here can explain how this is possible :D