The big fat extended battery is one of the things I miss from my HTC Universal from before it got stolen.
640*480 VGA screen, touchscreen, QWERTY keyboard - albeit a lousy one - 3G, SDHC, IRDA, Wifi, Bluetooth, 2 cameras, one for video, one for photos - that phone had nearly everything. And with the 4.8Ah battery I had, not only did the camera still work and so on, but it ran for a whole long weekend of heavy use on a single charge. I could leave home for work Friday morning, go away for a weekend, and it'd still be going when I got back to the office on Monday morning to charge it. OK, so, it was fat with the big battery and no longer fitted in its case - but totally worth it.
The only snags were the disastrous keyboard - poor layout, but app keys for the various bundled programs in the main alpha block, so if you didn't quite hit the space bar, you left your current app in mid-sentence and entered the web browser or something - and the fact that it ran Windows Mobile. Which is utterly horrid.
My current Nokia E90 does more and has a better keyboard, but it has no touchscreen, can't charge over USB, lacks a standard headphone socket and if I use it hard its battery is dead in 5-6hr. If I use my wonderful media phone as an MP3 player or radio all day, and navigate using its GPS, before sunset it's dead - and I can't charge it without the special Nokia charger. Old ones don't work, they changed the connector size.
If I tether it to my notebook it works fine as a 3.5G modem - but its battery is dead in 2-3hr of use.
And no extended ones are available.
It's so stupid it's tragic.