After too many charging cycles, the battery's capacity will be decreased. This is true for any Lithium-ion battery. Luckily the replacement of the battery in this device is very simple.
To open up the casing, you will need to unscrew the four Phillips #0 15mm screws which are accessible from the back.
Gently separate the two halves of the casing.
Disconnect the battery from the motherboard by lifting up on the white plastic tab on the top of the connection.
Gently pull the cord out by the white plastic adapter. Do not pull from the red and black cord.
Unscrew the Phillips four #0 15mm screws to free the motherboard from the casing.
Slowly pull the motherboard out of the casing. Make sure the loose battery wire doesn't get snagged.
Remove the four #0 15mm screws to release the battery housing from the case.
Take the battery housing and battery out of the casing.