What is C-rate?

C-rate is an often used term in combination with batteries. We explain what it means and how you can use this information to plan your battery storage.

C-rate or C is important for comparing batteries of different capacity (size). A battery with a larger capacity runs higher charge/discharge currents. Therefor it is rather difficult to compare ampere values. By calculating the C-rate, we take the capacity in kWh and divide through charging current. Further we can determine time for charging and discharging.

Time factor

A C rate of 1 is indicated by 1C. Using the example of a battery with 5 kWh, this means that the battery can discharged with 5 kW. Consequently, it is empty within one hour. A battery with a C-rate of 0.5 takes 2 hours to discharge. A battery with 2C can be discharged within 30 minutes.

It may well be that different C-rates are given for loading and unloading. Check out exact details in the technical data sheets of the individual manufacturers. It is important not to exceed the C-rate in order to ensure a long battery life.


Talking about GREENROCK salt water batteries they have a C-rate of 0.2. In other words one can say it is a 5-hour battery. That means it takes 5 hours until a completely empty battery is fully charged. The same value applies to the discharge.

Often a high C-rate is considered to be the most important specification of a battery. Depending on the application, a distinction should be made here. For example, the battery of your e-mobile needs a high C-rate so that you can charge quickly and continue your journey with a full battery after short breaks.

Conversely, with stationary home storage devices, such as GREENROCK – the saltwater battery, fast charging and discharging is less critical. These systems are designed for optimizing self-consumption. The solar power produced during the day is continuously fed into the battery. In the evening, the aim is to use as many hours as possible your own energy. Especially for these applications it is of an advantage use the capacity of the battery for hours. Low charging/discharging currents promote a long lifetime for any type of battery.

Comparison battery technologies

Here is a comparison of important key figures of different battery technologies. You can read more in our blog cost comparison of battery storage.

comparison batteries_EN