Be careful not to severely bend the battery or puncture it as it may leak potentially dangerous chemicals. Edit: THE BATTERY CAN EXPLODE AFTER THE LEAK OF FUMES. IF IN ANY KIND OF CONTACT WITH WATER, FROM INSIDE OF BATTERY, THE BATTERY WILL CATCH ON COLOURED FLAME. YES, COLOURED FLAME. IT’S A GOOD EXPERIMENT BUT ONLY IN ADULT SUPERVISION AND SAFETY

Using the plastic opening tool, pry the battery from the front panel until there is room to peel it off with your hand.

The battery is stuck on to the front panel with adhesive tape, so don't be afraid to use slight force when removing it.