Let me point it back to the topic for a moment
I would like to make SheevaPlug work on batteries, but not on daily basis (which has no sense - see post #2) but as a kind of UPS.
Plug would work with normal power support and if unplugged - stay up for 10 minutes on a battery pack. I could use small batteries as the capacity is not an issue.
It would save plug from accidental power outages and moving between sockets reboot.
All is needed is:
1. a set of small batteries (AAA would fit in the empty spaces in SheevaPlug I guess, but they can hang out
2. a tiny piece of electronics to kick in the battery source when the power is out and to keep the parameters good for the plug. (voltage can be reduced AFAIK)
3. a connector so that when PSU is plugged via the electronics (2) you can plug batteries whenever you want
That's the idea and I'm not an electreonics guy, so good luck. And if I make my friend solder it up for me I'll let you all know