Nokia’s “First True Windows Phone” —-Lumia 800, was beleaguered with battery related issues that were discovered late last year. To the relief of consumers, Nokia launched a fix that was released on January 19, 2012.
To get the update, one must connect to Zune. Lumia 800 will automatically inform you when your phone is available for update. The update also comes with Wi-Fi connectivity enhancements.
According to Nokia not all Lumia 800 are affected by the battery issue. You could check if you are affected by fully charging your battery and then dial ##634# to go to Service Menu. Go to Battery Status section. Check if you are utilizing a full 1000mAh, if not you are stricken by the problem.