I would personally go with a maxamps 8000mah battery pack. From what I read when I was going to do lipo (couldn't because of race rules), for the money you spend, you get a pretty good quality pack, and LONG runtimes. People are using this type of pack to run with nitros in there 20+ minute mains.
As for chargers, I was going to use a MRC 989 and those who I know have this charger and do lipos like it.
You will also want to pickup a liposack or battery bunker to safely store you packs, and probably a balancer too.
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