In a statement, Nokia has informed its users that a software problem in Nokia Lumia 800 is effecting some of its early users.
How to check if your Nokia Lumia 800 device is suffering from Battery issue or not ?
By Dialing ##634# you can enter the diagnostic menu where you can then select battery status. If your full charge capacity is lower than 1000 mAh then your mobile is affected.
How to Fix it ?
The good news is, its just a software glitch so it can easily be fixed with a software update. Nokia plans to deliver the update by early 2012 and mean while, if your phone is effected with the issue, nokia suggests you to charge the phone frequently to overcome the battery issue.