Battery is not charging.
Tablet was removed from cradle or cradle was unplugged from AC power.
Ensure cradle is receiving power. Ensure tablet is seated correctly. Confirm main battery is charging. The battery fully charges in approximately four hours.
Battery is faulty.
Verify that other batteries charge properly. If so, replace the faulty battery.
The tablet is not fully seated in the cradle.
Remove and re-insert the tablet into the cradle, ensuring it is firmly seated.
Ambient temperature of the cradle is too warm or too cold.
Move the cradle to an area where the ambient temperature is between 0°C and 40°C (32°F and 104°F).