"C" rating does matter. The "c" is referring to discharge. Take for example, if you have a 1000 mah battery, rated at 20C that means you can continuously draw 20(the c rating)X 1(amp hour rating) so you
Could draw 20 amps without harming the battery. Most battery's will have a slightly higher burst rating that will tolerate higher draw for less then 10 seconds. If you know your draw, it you can do the math. Do you know the draw? If that doesn't make sense, I can explain it better, or google it.