What is the voltage of your NiMH pack? That is an important piece of information that you omitted.

Each lipo cell has a nominal voltage of 3.7V. So 2-cell lipo pack is 7.4V, and a 3-cell pack is 11.1V. Right off the charger, the pack voltage will be higher than that, about 8.4V and 12.6V for 2- and 3-cell lipo packs.

The capacity of a lipo is specified in mAh (milli-Amp hours), the same as for NiMH packs. The larger the capacity, the long run time you'll have but the larger (and heavier) the battery will be.

The C rating tells you the amount of current the pack can deliver. Multiply the pack's capacity times its "C" rating.

For example, lets look at a 3300 mAh pack.

If the pack is rated at 15C, the maximum current it can deliver is:
3300 x 15 = 49500 mA = 49.5 A

If the pack is rated at 12C, the maximum current it can deliver is:
3300 x 12 = 39600 mA or 39.6 A

If the pack is rated at 20C, the maximum current it can deliver is:
3300 x 20 = 66000 mA or 66 A

- Jeff