How to test your Mobi or DualBoard Pen Battery
1. To access the pen battery, you will need to first remove the back pen cap. Do this by pressing the notch between the charging rings and the flat end, on the back side of the pen, then gently slide the cap off.
2. Inside the pen the cylindrical green object is the battery (half-cell AAAA NiMH battery). Gently remove the battery, and check for any disconnection or corrosion on the battery or in the contacts and replace the battery without replacing the end cap. (You can easily rub the ends with an eraser to check for any light corrosion, which may not be easily visible to the naked eye.)
3. When the battery has been replaced, hold the pen with the blue stripe facing toward you. Depress the rocker switch on the pen. You should see a red light, in between the charging rings, and it should flash 4 times. This flashing indicates a battery with a full charge. No flash indicates the battery, or its connection to the pen, has failed.
4. If possible perform the same test with another battery from a pen that is known to be in working condition. If the light does not flash with the new battery installed, then this is an indication that there is corrosion on the contact points of the battery connection, or the pen is bad and will need to be replaced. If the light flashes, with a battery from a known-working pen, it is only the battery that will require replacement.