18650 C Rating-Definition and Test

18650 lithium batteries are a common type of batteries that are mainly used in flashlights, laptops and other portable electronics devices that use rechargeable batteries. There are several parameters used to rate these batteries and whenever you’re buying any of these batteries you’ll need to know some of these. The commonly known parameters by most people are the voltage and capacity of the battery.

However, there are other important parameters that affect how the battery performs. One of these parameters is the c rating of the battery. In this article, I am going to briefly share with you everything you need to know about c rating of 18650 batteries, definition and testing

What is c rating in 18650 batteries?

C-rating of a 18650 battery is the measure of the rate at which a battery can be discharged relative to its maximum capacity. This means a battery with a higher c rating is capable of discharging more current at a time than a battery with a lower c rating. So, basically the c rating of the battery is meant to let you know how much current can be drawn out of the battery at a time without creating any negative effects on the battery.

If you discharge the battery beyond its rated discharge capacity, it will overheat which eventually leads to immediate and long term negative effects to its performance. So while you are buying a 18650 battery, it is important to know the size of the load where the battery is going to be used so that you compare it with the maximum discharge current of the battery. The battery c rating and the battery capacity will help us determine the maximum discharge current.

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It is important to get a battery whose maximum discharge current is above the required current by the device that we intend to power up. For example, if we have a 18650 lithium battery with a capacity of 2000mah and a c rating of 1C. This simply means the battery is able to provide constant current of (2000x1) ma for 1 hour without any issues. In simple terms a 1C rating means a 1-hour discharge of the full battery capacity. A 2C rating means 30 minutes’ discharge of the full battery capacity.

If we consider another battery with the same capacity as the above but with a c rating of 2C. It means that battery is able to provide (2x2000) ma =4000mah in 30 minutes. If you connect a load that needs more than 4A on such a battery, the battery will start overheating which is not a good thing as far as its overall life is concerned.

What is c rating in case of testing 18650 battery?

The c rating of the 18650 battery will help you determine how much current you can discharge from the battery in a specific amount of time without causing the battery to overheat. The c rating is determined by constantly discharging the battery and finding out the maximum current it can discharge in a particular amount of time without causing any negative effects on the battery.

The battery capacity values you normally see written on the batteries are rated at 1C. For instance, a battery with 2500mah means this battery is having the capacity to discharge 2.5A for 1 full hour before it gets totally discharged. But in some instance, some batteries don’t have that capacity to deliver that much current in an hour that is why some are rated with a c rating below 1C. For example, if a battery with 3000mah is rated 0.5C, it means such a battery can discharge a maximum of 3000/3ma =1500ma in 2 hours. Anything beyond 1500ma will cause the battery to overheat and also affect its overall battery life.

What is the best c rating for 18650 batteries?

The c rating for the battery you choose should highly depend on the current needed by the device you intend to power up. Before buying the 18650 batteries, make sure you know the current you need first. It is from this that you will be able to determine the battery capacity and the c rating you need to safely discharge the battery without causing any immediate and long term damages to the battery.

However, if in some way you have no idea of the current needed by your device, choose a battery with at least 1C rating. Like we have seen above 1C means you will be able to discharge the entire capacity of the battery within an hour. So the current you will get from the battery will basically depend on its capacity.

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In most cases, 18650 batteries(cells) have a capacity ranging from 1800mah to 3500mah. With a 1C rating, it means your device will be able to use up to at least 1.8A without causing the battery to overheat. From a practical point of view, 1.8A is enough for most of the electronic devices that use these batteries. Most of them actually need 500ma which means a 18650 battery can last more than 3 hours of use on a single charge.

Final Thoughts

The c rating of 18650 batteries is an important aspect to look at before you buy the battery. Just like we have seen above it is the c rating that you use to gauge how much current the battery is able to give you in an hour. Batteries with higher c ratings are more desirable because they give you room to use the battery in a wide of devices that consume different amounts of power without worrying that the batteries will be damaged.

However, one important thing to note is that a good number of sellers are not honest about the battery capacities and c ratings of the batteries they’re selling. That is why it is important to get a battery with a c rating way beyond what you require. This is because if the actual c rating of the battery is slightly lower, your battery will still have chances of being in the safe zone of discharging.