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What is C-Rating?

This entry was posted on 21/07/2020 02:20:09 PM by Valen

What is c-rating

C-Rating is an informal way of describing how much current the battery can safely deliver. 

But what are C10 and C20? Is there a difference? Which one do I pick for my system? The team at Valen are here with information to answer your questions. 


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So, what is C-Rating?

When describing batteries, the discharge current is often expressed as a c-rate to normalise against battery capacity, which is usually very different between battery brands and sizes. 

A c-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. The letter 'C' in these expressions is more easily understood if you think of it as simply the value of the Amp-hour rating. 

You can use the capacity of the battery and the c-rating of the battery to calculate how many amps it can constantly discharge until it's empty. 

For example, if you take a 100Ah battery and divide it by it's c-rating, C10, you get 10A or 10amps. So this battery can discharge 10A for 9 hours until it's empty without overheating. 


Different C-Ratings

For the same battery, the battery capacity varies per c-rate. The faster the battery is discharged, the smaller the capacity is. This will vary per battery type and chemistry. 

Two batteries that have different capacities and different c-ratings can have the same discharge capability. 

For example: 

  • 12V180Ah battery at C10 = 15.8A
  • 12V90Ah battery at C5 = 15.8A

However, they won't last the same amount of time!

  • 12V180Ah battery at C10 = 6 minutes
  • 12V90Ah battery at C5 = 12 minutes

Looking at the Ah data of the battery drop down the hours until you find the equivalent capacity in hours. 

C Rating table


Do you have more technical questions on batteries?

If you have any questions regarding an upcoming project or past battery system, the Valen team are here to support you. With customer service being one of our core values, we go above and beyond our clients. 

Simply click here to get in touch with Valen!

Written by Valen

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