Hey guys.. Kindly check out this nice little Arduino compatible board from eNTesla
eNTuino Atmega8 version : http://entesla.com/development-board/arduino/entuino-arduino-atmega8
eNTuino Amega328 version: http://entesla.com/development-board/arduino/entuino-arduino-atmega328
What makes it different is that it has an on-board battery charging circuit for Li-Ion batteries.