I used to have a similar issue. I installed osso-statusbar and realized that my CPU usage was abnormally high, about 80%. Depending on how many applications I have running on my N800 the normal utilization is around 10%-20%.

My CPU usage was high because of the metalayer-crawler process was using about 70% of the CPU which was causing the battery to drain alot quicker. I would suggest installing osso-statusbar, or if you have xterm installed you can do a top, either way see if there is a high CPU usage and if so see if there is one process that is using most of the CPU. If a process is taking most of the CPU and depending on the what the process is depends on what steps to take next.