I read battery life is 3 hours. Anyway to extend that - spare batteries , fuel cell ?

Spare batteries would work. But that 3 hours is quoted with constant, always-on, always-using, wireless LAN access.

I have read somewhere that the battery (which is standard Nokia stock) can be replaced with a model with more capacity.
But you shouldn't worry about battery life. 3 hours is for constant WLAN connection, which drains battery. Three days for normal usage (a bit WLAN, a bit offline, most of the time idle) is more realistic.

I asked about the batteries from a retail shop. They are same batteries which are used in communicators. Around 50 euros per battery. Not too expensive (I mean batteries for cheap laptops cost 2-3 times as much and give only the same 3 hour usage time)

I wouldn't stress about the battery life too much. I'm getting MANY hours out of a charge. 3 is extremely conservative. 5 to 10 is more realistic.

If you play music you'll get around three hours on a full charge.

The first day, I charged my battery, it lasted for about 4 or 5 hours... (while using wifi...).
From then on, with a full charge I never get more than 2 hours... (with wifi)
I even tested it: full charge.. turn on, play some games for 10 minutes.. turn off.
the next day... turn on... surprise... only 2 bars on the bat metter.... and about an hour of usage....
(It also takes a long time to recharge... 3 to 4 hours...)

I have understood that the batteries can stand it if you charge em even if they arent totally empty. (please correct me if im wrong)

If you buy a few extra batteries, you may need 2 per day, 3rd one for extreme days. Well, when you get home, just charge the first battery and before you go to sleep put the another one to charge for night.

I havent got the device yet, but I habe been thinking it will be something like that for me.

You're quite right: the batteries are Li-Ion or Li-polymer, meaning that you should continuously top-up the charge and avoid deep cycles (completely discharging them and recharging from empty).

I found this thing called a "cell rescue" it was on clearance at compusa for like 1.94 or something. it takes 3 AAA batteries and can charge a Nokia phone. I use it with a CA-44 and it can power the 770. This could be one idea use some velco or something to attach it to the back of the 770 or something. Plus it has a built in flashlight, lol. Here is the link to compusa.

http://www.compusa.com/products/prod...310&pfp=SEARCH