The (ground based) battery
Since my aim was to make the ground based portion of the system portable, I needed something to power the receiver that I could carry.  I selected a 2.3AH gel cell battery.  This battery is the perfect size and shape to fit in a small butt pack, yet offers more than enough power for a full day's flying video
Battery considerations and options
The receiver can be powered by virtually any 12v dc power source.  If you opt for a less portable ground bases system that uses a small TV and VCR, you will probably have access to a very high capacity battery like a car or 'marine' battery.  If your tv and vcr are powered by 110 volts and you end up going with a power inverter, you can simply plug the receiver's small 'wall wart' into the inverter.

 
Construction Details
I opted to solder a Sermos connector onto my battery, and then make an adapter cable to plug into the receiver.  This way I can charge the battery directly from my RC battery charger, which has a Sermos connector attached to it.  NOTE that if you plan on doing this, your RC battery charger must be rated to charge Lead Acid batteries!