Also:

• How long have you had your tablet and--more importantly--your tablet's battery?
• If your tablet is a recent purchase, did you buy it new, open box, or used?
• Is your tablet's battery of genuine Nokia make, or is it an inexpensive purchase from eBay or the like?

Your tablet's run times sound like those my N800 managed after I heavily used and abused its battery for about a year. With a new, genuine Nokia battery, happiness returned.

I specify "genuine Nokia battery" because your run times also sound like those provided by cheap knock-off batteries commonly sold on eBay for a few bucks. On the plus side, the cheap eBay batteries do often come with a desktop battery charger...that probably won't short out and burn down your house.