I have to leave my Arduino Mega unattended for as long as possible for remote camera control. It also has a cellular shield attached. http://www.sparkfun.com/products/9607.
Would this battery be compatible with the Mega? Right now for testing, I am putting 9V through the VIN (6 AAA's).
Looks like the shield could draw a little bit of current during transmissions
Off mode: <100uA
Sleep mode: <2.0mA
Idle mode: <7.0mA (average)
Communication mode: 350 mA (average,GSM)
Communication mode: 2000mA (Typical peak during TX
slot,GSM)
With 6 cells, I think you're going to be ok. The Li-Ion cell packs have a board under the wrapper that I think enforces load sharing, so even with bursts of 2000mA, no one battery sees it all.
I'm not sure if this is a stealth project or what exactly, but depending on where you live or where it's going to be, solar could be a possibility to charge whatever batteries you do run to allow/extend the un-attended operation