There are basically two modules, the transmitter and the receiver.
The receiver uses one of my own PCBs which is essentially a jeenode with an added uSD card slot, the display is from Jeelabs and is designed to sit directly on top of a Jeenode but it's not the cheapest display you can use. The receiver can also be made using a standard Jeenode instead of my PCB.
I run the transmitter off some old lithium rechargeable 1850 cells taken from an old laptop battery, the receiver also runs on a lithium battery from a mobile phone but you can use any batteries you like from 3 to 5 V.
The battery voltages of both the transmitter and receiver are monitored and displayed on the LCD, the code for the battery monitoring was taken from the Jeelabs blog here and the sleep functions were also from the same post using the Jeelib libraries.
Sketches can be downloaded for transmitter and receiver.
Any questions or comments, feel free.