What is C-Rate?

Charge and discharge current of a battery is called C-rate. For example, 1C is the battery capacity for 1 hour fully discharged. A 2400mAh battery has a 1C of 2400mAh.

Example 1:

• 1C from a 1000mAh battery is 1000mAh of current for one hour if discharged at 1C rate.
• 1C is often referred to as a one-hour discharge.
• a 0.5C would be a two-hour, 0.25 C would be for 4 hours.
• a 0.1C a 10-hour discharge.

In other words C-rate X hours = 1C, therefore 0.25C X 4 hours = 1C.

Example 2:

The same equation can be used for high discharge that occurs in less than 1 hour. Let’s assume the following examples for a 2500 mAh battery:

• For this battery is C = 2500 mAh
• At 2C, the battery is delivering 2 X 2500 mA = 5000 mAh.
• Therefore the duration of the 2C discharge is C-rate X time = Capacity, 2C x 0.5h = 2 x 2500 mAh X 0.5h = 2500 mA.
• At 4C, a 1000mAh battery would deliver 4000mA for 15 minutes.

C-Rate Reality:

• C-Rates provided my manufacturers are based on slow discharge of 0.1 to 0.25C.
• Higher rate discharge results in less total Current ( or Capacity ) being delivered.
• Higher rate discharge causes internal energy losses and a voltage drop.
• The battery reaches the low-end voltage cut-off sooner at higher C-rates.

C-Rate Reality Check:

• Assume you have a 2500mAh NiMH battery. C = 2500 mA.
  
• At 0.1C you can reasonably expect 250 mA for 10 hours ( 0.1C x 10 hours = 250 mA x 10 hours = 2500 mAh ).
• In theory, your NiMH rechargeable battery operating at 0.5C should give you 1250 mA for 2 hours ( 0.5C x 2 = 1C = 1250 mA x 2h= 2500 mAh ).
• Reality: A very good NiMH battery might yeild 0.5C for only 1.8 hours.
• This would give you 0.5C x 1.8h = 0.9Ch. C in this case is 2500 mA so your NiMH battery would only deliver 1250 mA x 1.8h = 2250mAh.
• The higher your C-Rate, the less total energy is delivered.
• This is true for all batteries.
  

Quality is not only a measure of what the rechargeable battery actually delivers. You need to consider how the rechargeable will perform at higher C-Rates.

Some rechargeable batteries don't even deliver 1C from the get go. Check out the performance test results !