Basically what the c rating is when you are talking about charging it, you take the mah of your pack and divide it by 1000. The number you get there is what 1c is. So 1c for your pack is 5.2, if you charge this pack at 1c you are charging at 5.2 amps. So at 5c....you get the picture, over 25 amps. For a 2s pack that is overkill and some tracks even have rules about how many c you can charge your packs at. It can become a huge fire hazard.

Now if you want to charge those 4s packs for your mugen I would definitely get a power supply around 15 amps or more, it will supply better wattage and let you get the amps up for those big batteries. Hope that helps