Nokia has just confirmed that the expected battery fix update for the Nokia Lumia 800 has now began to roll out. If you are new to Windows Phone platform you should know that as always all devices will not get the update at once. Microsoft always pushes the updates slowly over a time period and in groups. It could take upto 2 weeks from today for the update to be available for your Lumia 800
When the update is pushed to your device you will get a popup message asking you to connect your Lumia 800 to the Zune client on your desktop. You can also have a look at the Nokia Product Support page if you are facing some issues with the update.
What does the update improve on my Lumia 800?
The update will bring the software on your phone to version 1600.2483.8106.11500 which has:
Besides the above improvements the update would also include other fixes which was mentioned by Microsoft a couple of weeks back
Personally I have not received the update yet on my Lumia 800, so I cannot confirm exact improvements made to the battery. I would be updating this post or making a new post as and when I get the update pushed to my device.
UPDATE January 20th, 2012: The update has just been pushed to my Lumia 800. I can confirm that the battery indeed has been fix to recognised to read as 1400+ mAh, plus as you can see from the image below it is fully charging @ 100% and not lower.
source: Nokia Conversations