C = equal to (full) capacity. If the capacity of the battery is 2000 mAh and you charge at 1C it will be 1* the capacity of 2000= 2000mA. This means the charge will take 1 hour to charge the battery.  If you see a .5C it means half of the capacity so in this case the half of 2000 = 1000. So at half the charge rate, it`s taking 2 hours to fill. Another way to remember it is to say, 0.5C is 0.5 times the capacity. 0.1C is 0.1 times the capacity. A little help: Try to see 1C as 100% charge current. 0.5C is going to be 50% = 2hours 0.2C is going to be 20% = 5hours 0.1C is going to be 10% = 10 hours 0.05C is going to be 5% = 20 hours