I agree that the battery status messages seem fairly useless. My 800 has been behaving much like febb describes since my upgrade to OS 08. At the same time, my battery life seems to vary from being usable for about 1 hour to 2 1/2 hours.
Alternately, my wifes new n800 with the same OS has much better battery life. So, it's obvious to me that part of what is going on is that the original batteries just don't seem to have a very long service life. I had two Nokia batteries. I had purchased an extra Nokia branded battery. So, after just one year both batteries need to be replaced?! WOW!