I finally ponied up for an ev-do card to make sure that I have no excuse for missing a post short of being trapped in a hole by bizzaro superman.
If you remember the diy ups, you might like the attach a giant battery to a stock ups version. I did this myself years ago. It works well, but use a maintenance free battery to minimize hydrogen off-gassing. In fact, I’d suggest some proper ventilation for the battery pack. Miata batteries have a vent tube if you want to keep the parts count to a minimum. (but they are a bit pricy)
Something a little oldschool – [Alexandre] added a serial port to his newton message pad 2000.(Not in english, but easy enough to understand.)