My battery packs are rated at 3500mAH. Gives me 8 to 15 minutes run time. There is no right or wrong answer on which batteries to use - - as each battery (or series of batteries) has its advantages and disadvantages. If long run times are most important to you, you probably should select gel cell batteries with high amp ratings. (If you are interested in a 7v battery - - make sure to get two and run them in series to equate to 14v - - - as 7v will not give you very good speed on such a big boat.) If speed is most important to you, I recommend increasing the voltage to the maximum amount your motors and speed control can handle - - and use NiMH (stick) batteries to reduce weight. The drawback to NiMH is usually run time and $$$. Getting the right speed control is also critical in determining performance. I skimped on motors and splurged on speed control. The results, so far, have suited me fine. It's fun, however, to experiment (and costly unfortunately).