Unscrew the two Phillips #00 screws on either side of the device, on the sliding handwriting panel.

Slide out the handwriting panel.

Insert a paper clip into the two marked small holes on the back and push downwards while pulling the handwriting panel gently.

You should see the buttons connector, like the third picture.

Gently remove the handwriting panel from the device.

Be careful - it's still connected by the button cable. Peel the cable from the device carefully with a spudger - it is attached with a little bit of adhesive.

Carefully remove the connector and set the handwriting panel aside.

Remove the two Phillips #00 screws on the back of the device.

Unscrew the two small Phillips #00 screws at the other end of the device.

A small metal part will fall out of the device from the other side. Keep hold of this - you won't be able to put these screws back in without it.

Using a spudger, gently separate the back casing from the rest of the device.

Be careful - the back casing contains the battery, which is connected by a very thin battery cable.

Lay the two halves side by side.

The battery is usually held to the case by a small amount of adhesive. Carefully peel it up with a spudger.

Lay the back case aside.

You should now be left with the front panel and the battery.

Gently disconnect the battery connector. It's very small and the pins are very delicate, so be careful not to bend it.

When you install the new battery, you may find it useful to secure it to the back casing with some blu-tack, double-sided tape or even a small amount of glue.