Best racing batteries for a revo?

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I just converted my revo platinum to electric and need to know what the best packs would be for racing? I am currently running A123 4s2p and this is only good for 12.5min I really need to get 15min at the least. the truck has the mechanical brakes, Quark 125b esc and a ammo 36-50-2300 or a 36-56-3600 motor. The problem is I have to stay at 14.8v or less for RC Pro.

I could run right with the guy that I have been battling with in the state series last weekend on my first try with the electric but I had to go back to nitro for the race this week because of the battery issues.

Any help would be greatly appreciated.