With normal use, the single AAAA alkaline battery for the digital pen will last an average of 6-12 months. This is a standard battery that is available from a local retailer.
To change the pen battery:
Unscrew the barrel , the lower end of the pen, counter-clockwise from the front section .
Remove the old battery  from the barrel.
Place a new AAAA battery into the barrel with the positive (+) end facing the front section .
Screw the barrel clockwise onto the front section until tight.
Confirm that the pen is working by turning on the digital notepad, and tapping the pen on the tablet. The green Activity indicator should blink, and the pen symbol appears in the status display if the notepad receives a signal from the pen.
Warning: When the front section is unscrewed from the barrel, DO NOT TOUCH the piece of metal (an electronic transmitter) that extends beyond the edge of the front section . Doing so might damage the pen and adversely affect its performance.