A few days back Nokia confirmed the battery issues with the Lumia 800. Plaffo.com has managed to get an exact date. The following memo was given to officers at the 3 Store Italy by the carrier authorities:
"Subject: WARNING: Problem Nokia Battery Lumia 800 for the only colors Cyan and Magenta.
Nokia has revealed a limited duration of the battery to the software problem Lumia 800
only for the Cyan and Magenta.
As of January 18 there will be a sw update that will also apply directly to the end customer.
Meanwhile, if the customer insists on the immediate solution of the problem proceed as follows: Open a SAT warranty notes indicating "Battery Problem". The terminal will be replaced with a new terminal"
Although the memo say for the colors cyan and magenta, this is not entirely true as I personally own a Black Lumia 800 and am facing the same issue. There are other reports on the internet which supports the conclusion that the all the three colors are effected and not only cyan and magenta.
To check if your Lumia 800 is effected with this issue follow the process given in this earlier blog post. If your full charged capacity shows around 970-980 (less than 1000 mAh), your phone has this battery issue.
Currently I am charging my Lumia 800 twice a day with minimum use. More details as and when the update starts to roll out.
UPDATE January 18th, 2012: As promised, the update is now been pushed. More Info here
(memo source: plaffo.com)