If your going with seperate batteries save yourself some weight and hassle and run your ff off of rechargable AAs. It will run it all day, and weigh a fraction of the weight of even the smallest gel cell. You can also use regular AA's if your in a remote area where charging isn't possible. I ditched the gel cell a while back and there is no going back. If you are interested in trying AA's I wrote a short tutorial on making an AA power supply here...
http://www.norcalkayakanglers.com/in...d=29&Itemid=42