1. Turn your Compaq V3900 laptop over.
2. Find the laptop battery release button lock for your Compaq V3900 laptop.
3. Now that your Compaq V3900 laptop battery is unlocked, find the battery release button down.
4. Holding the laptop battery release button, gently pull your battery away from the laptop.
5. Now that your Compaq V3900 battery is removed, grab your replacement Compaq V3900 battery for installation.
6. Insert the battery into the slot. Push the Compaq V3900 battery towards the laptop and secure it in place.