A high capacity 4s-6s battery will be cheaper and easier to transport. I have a 4s 16000 and barely last the day with practice. I think others are using 5s or 6s, those will definitely last you the whole day with practice. Double check with someone who is currently using that setup before buying. I think Korey Harbke is using a 6s battery.
Hobbyking, which has a warehouse in Oregon, sells large capacity batteries.