Do you ever wonder about what's inside a wacom tablet pencil and how it works? mine has being inside water some seconds and stopped work. This is what i did...
First, carefully pull off the little plastic piece number 1. You must use a knife or something with sharp edge to wedge.
After this, you are ready to disassemble pen's exterior case, pulling strongly between parts 3 and 4. If it's hard, you can turn pieces 3 and 4 between them, but only a bit because electronics inside has a guide that lock it into the case.
This is what you are going to find inside. Next step is release primary and secondary buttons (piece nº 2) pulling up straightly and softly, being carefull do not break a and b parts that hold the button.
Other piece we must take care is piece number 5, which is quite fragile because is glued to the board through 2 thin wires that could brake. This part keeps wet around the wire and we must dry it perfectly keeping it warm.
Point number 6 shows how board engages the pen case. This is why we might no turn too much pieces 3 and 4 between them in step 1 to keep us avoid to break the circuit board.
And here is what's inside a graphic tablet ballpen and what i've broke disassembling.
I hope this tutorial helps you, now that you know what's inside a graphic tablet pencil, you'll gess which is your trouble.