To get the battery out, you have to take out the right side radiator.

Notice there is two plastic latches, you need to lift both up using some small metal part as the leverages.

While both latches are up and hold the speakers, trying to turn the radiator anti-clockwise.

This can be hard as first but no worry and there is no cable connected to the radiator.

As you turn about 1.5cm (or can not turn further), just take out the radiator cap.