Well I use a EverStart 12V High Power Lawn & Garden battery that I bought at my local Wal*Mart. Works good for me and I also recharge my 12V batterys with an EverStart Basic Battery Charger that is a 1 AMP Trickle Charge charger. I also bought that at Wal*Mart.
I also know some people use little 12V batterys made for this hobby like the one at towerhobbies.com that you can view by clicking the link farther down in my post. I don't know much about them but I think you recharge them every time before you use them. Thats why they are so small, because they hold 12 volts for a short time unlike my bigger, bulkier battery that holds 12 volts for a very long time. Another thing is that I DONT use a field box to store my batery. If YOU ARE going to do that then I would sugest the small one! So hopefully I helped you in some way!

The battery at towerhobbies.com------------- http://www2.towerhobbies.com/cgi-bin...?&I=LXL370&P=7