It's best practice to keep your second battery charging in the hub at all times. That way, it's already fully charged when it's time to do a battery and cartridge change.
- Press on the indent on the top of the hub to open it
- Place the battery in the battery slot as shown. Make sure that the gold contact line up.
- Close the lid of the hub
- The LED will turn red to indicate the battery is charging.
- Once the battery is fully charged, the LED will change to green.