I am just curious. The IT is good enough for my daily use, only complain is the battery lasts less than 3-4 hours when wifi is on.
I hope there is a portable browsing machine that the battery will have 10+ hours of wifi use, so I don't have to worry about charging or extra batteries every day.

You could upgrade to the mugen 3600mah battery

http://shop.eten.hu/mugen-power-3600...lue-p-475.html

I've got one of the 1800mah mugen batteries and it works as good if not better than the original nokia battery. It might add a little bit of size to the N810, but if battery life is what you're after, battery life is what you'll get.

Do you have a really old wifi router? I remember my n800 battery was drained within a few hours os inactivity when it was connected to that old wifi router of mine (can't remember what model it was). Obviously, there was something in it that stopped wlan energy saving to work on the tablet.

Since I got a new router (long time ago) and replaced the battery with a new nokia bp-5l (recently) battery life is great - several days of moderate use or one day of really heavy use.

Yeah, I'm not clear on whether the OP means "idle time on WiFi" or "active use". Either way, a router that doesn't support PSM will reduce battery life, but more drastically in the former case than the latter.

Buy one of this: http://dealextreme.com/details.dx/sku.8079 and a couple of rechargeable AA batteries. The stock battery's capacity is 1040mAh I think, and you can buy 2800mAh AA batteries. That should do it.
I haven't tested yet if this charger can give power faster than the N8x0 uses it, but I hope yes.

szucsati, sorry it won't. I picked up the energizer branded version of that. When it's plugged in it looks like it is charging but it doesn't. The tekkeon 1550 is more expensive but it is a better buy.

Actually, it probably won't. I don't know what they use to up the voltage (hopefully a switching regulator), but it will certainly significantly reduce the amperage available. Your best bet is a 4xAA battery charger, as it inputs the same voltage the tablet needs. And even then I find it difficult to completely charge the tablet's battery from it.

Also, the battery-to-battery charging process isn't exactly hyper-efficient (OTOH it's not especially bad either), so don't count on all those amp-hours from your charger to make their way into your tablet's battery.

I've got one of the 3600mah Mugen batteries and I love it! I could run for days with it on just average use. The only thing that sucks is the plastic cover, and nobody will make a metal one to replace it.

Yeah, my bet is that this is to blame. Power-Saving Mode is critical for a device like this. If it's disabled (or not supported) either at the access point or in the tablet's control panel, you're screwed.

I've been quite happy with the battery life on my n810, and I leave wi-fi on (with PSM) all the time. I'm not a heavy wi-fi user, but just idling and browsing a few sites leaves me with a full battery even after 16 or so hours off the charger. Normal browsing doesn't seem to have much of an impact on battery life either, since most of the time you're reading the screen rather than transfering data. (Streaming and flash-heavy sites are another matter, though!)

And no worries about wi-fi performance with PSM, either. I've never had a problem opening an ssh session from my PC to my tablet, even when the tablet has been completely idle for hours and is in maximum power-saving mode. It still gets a beacon from the access point a couple times a second, so you won't notice a lag going from idle to active.

Another good battery-saving wi-fi hint is to increase the WLAN search interval. I have mine set to 10 minutes, which means that when I lose the wi-fi signal the n810 only searches again every 10 minutes.

Mind you, Bluetooth might be a killer. I don't have Bluetooth enabled, and I'm not familiar with how it handles power control. If it's enabled and it has a hard time maintaining contact with your phone, that could potentially be a big power drain. (Just speculating.)

In my experience, CPU tends to be the biggest power drain. If you're doing something CPU-intensive (which may include streaming media, depending on the codec) the battery is only going to last a few hours. If the device is warm to the touch, you're draining the battery quickly.

is there a list somewhere of routers that do well at supporting PSM?