Go to radio shack or Fry's..
Get one of these battery holders:
http://www.radioshack.com/product/in...ductId=2062242
And one of these connectors:
http://www.radioshack.com/product/in...ductId=2062218
The snap connector will connect directly to the battery tray. You can hard wire it to your FF. I use rechargeable AA batteries. Simply pop them out of the tray to charge.
I also use somthing similar to this : (from walmart)
http://www.snapware.com//product_buy.asp?dept%5Fid=7001
The battery tray fits inside of it. It snaps closed with a rubber seal. I put that into a dry bag and roll it up. Never had any problems.
Don't forget dialectric grease for the connection between FF unit and cords to prevent corrosion.
This is a good setup, however I might switch over to this type of battery to get longer life between charges:
http://www.frys.com/product/2855784?...H:MAIN_RSLT_PG