10-4 - this is a good 1st read about lipos -

http://www.rchelicopterfun.com/rc-lipo-batteries.html


Run times are mainly a function of capacity - its mewasured in mah and is usually the big number talked about when battery is mentioned - like a 2S 5000mah 40C lipo. Genberally get the biggest one that will fit in your RCs batt tray without disturbing balance an adding too much weight.