One of my friends owns a white macbook and recently the battery has just not been recognized. Up at the top where there should be a battery symbol has been a black x in the picture of the battery, so the comp only runs when plugged into AC power. The battery wasn't charging or anything so it wasn't coming out of low battery mode. I tried reseating the battery, checking the screws in the compartment, cleaning out the contact points, and resetting the PMU to no avail. What else can be done?