C-rates are useful in determining which battery is best for your operation, e.g. Table of battery comparison, especially in conjunction with the battery capacity.
Battery capacity is the Amp-hr (Ah) rating of a battery and describes how long a battery can provide a certain current (A). For example, a 100Ah battery can provide 100 Amps to a system for 1 hour (100A x 1hr = 100Ah), or 50 A for 2 hours (50A * 2hr = 100 Ah), or 10A for 10 hours (10A * 10hr = 100 Ah).
C-Rate is a measure of that battery capacity rating. A battery that is rated to discharge its total capacity (Ah) in 1 hour would be rated at 1C, or in 2 hours would be rated at .5C, or in 4 hours would be rated at .25C, or, in the faster direction, in 30 minutes would be rated at 2C. See Table 1 for some examples.
Because of internal resistance loss and battery chemistry, a battery rarely delivers nameplate rated capacity in only one hour (1C) and typically maximum capacity is found at a lower C-rates. Plus, faster charging and/or discharging (aka at a higher C-rate) typically reduces the total capacity and lifespan of a battery. 
|C-Rate||Rated Capacity (Ah)||Average Current (A)||Charge (or discharge) Time|
|5C||50 Ah||250 A||12 min|
|2C||50 Ah||100 A||30 min|
|1C||50 Ah||50 A||1 hour|
|.5C (aka C/2)||50 Ah||25 A||2 hours|
|.25C (aka C/4)||50 Ah||12.5 A||4 hours|
|.1C (aka C/10)||50 Ah||5 A||10 hours|
Battery manufacturers often publish datasheets with graphs showing capacity versus C-rate curves. The C-rate is also used as a rating on batteries to indicate the maximum current that a battery can safely deliver in a circuit. So a battery rated at 1C on the battery, indicates that it can safely discharge its full storage in 1 hour. Some batteries, e.g. Lead Acid Absorbent Glass Mat (AGM), typically have a low C-rate of about 0.25C (safe and efficient charging or discharging of the rated storage over a 4 hour span), where as other batteries, e.g. Lithium Iron Phosphate (LiFePO4), can have a high C-rate of over 3C (safe and efficient charging or discharging of the rated storage in just 20 minutes!).
See more[edit | edit source]
- Table of battery comparison
- Battery temperature to capacity tables
References[edit | edit source]
- Battery University - What is a C-Rate