[aiharkness]

You should not have a problem with a stock theme. While it may not be impossible for a third-party theme to interfere with the charging functions (or the displayed indicator), that wouldn't be my first, second, or third guess.

Check and make sure the battery is tight in the compartment. Make sure the terminals are clean and not corroded. Try a new battery, or at least try another battery that is known to be good.