Just found this quote from Nokia Support on the WMPoweruser web site addressing the reported issues with the Lumia 800 battery life.
“We understand that some people have expressed concerns about battery life on the Nokia Lumia 800. Early investigations show that most people are enjoying the full Nokia Lumia experience without any problems and we have not been able to identify a single root cause that would lead to erratic battery behavior at this stage. A software update in early December will make some improvements to power efficiency, while a second update in early January introduces high voltage charging, increasing the Nokia Lumia 800’s battery power from 1300mAh to 1450mAh. These are scheduled improvements and will enhance the overall experience, but are not designed to address any issues that may be occurring with individual products. We recommend that anyone who has concerns contact local Nokia care representatives at their earliest convenience.”
It will be interesting to see how much difference this makes.