How do I replace the internal battery?

1) First remove the screws on the side of the device. 

2) Pull down the back cover and remove the battery that is already inside. 

3) The Battery has grooves on the + side and is smooth on the - side as shown below in the picture. 

4) Insert battery with the + side on the left with the - side on the right as shown below.

5) Put metal screen back on and screw in the screws.