You know, I swear Bunnie had a blog page w/an Infocast annotated board image. It was a Infocast verses Chumby page. Where is that???
Any how ... I was looking at that page for 10s of minutes. I (think I) recall the LION charging chip is missing on the Infocast board as well (maybe there isn't even a target for it). Note, LION batteries are probably the best secondary batteries. But you can not (easily) buy them loose because they need to be managed. For example, you would get about 1 cycle out of them if you put LIONs into a flash light and ran them down. So they are usually sold in packs which includes a management (charging) chip (processor) of some sort. That chip (among other features) will shut down the connected device before permanently damaging the LION cells due to over discharge. If this chip is missing from the Infocast it would be difficult to re-integrate.
Instead, if I really wanted my Infocast to be (somewhat) portable, I would look into one of those "run and/or recharge your USB appliance with our power pack" devices. The Amp-Hours these cell-phone-size packs now provide is incredible. Be cautious, but I believe the Infocast runs on 5 volts which is what I believe is supplied over the USB port of these "power packs". Buy definition I believe USB ports are only required to supply 500mA and I believe the Infocast power supply is rated at 2Amps. So some power packs may not work, or, worst be damaged by the current draw.
Sorry about all the "I believes". But I have not done this so I can not say for sure it will work and / or not damage your devices and / or not harm you. Remember Lithium is nasty stuff. Modern batteries should be safer. But Lithium was probably the cause of many a laptop fire.
-good luck