• SolarKobo

Battery C Rating Explained

Updated: Jul 7

The C Rate is derived from Coulomb’s Law developed by French physicist Charles Coulomb, known for the famous Coulomb's law. The C-rate is a way of measuring what time, in hours, at which a battery would be discharged.


A “C” rating is simply a battery’s capacity when discharged over a specific period of time.

This rating is acquired by adding a specific size load to a battery and allowing it to discharge completely in a 3, 5, 8, 10, 20 or 100 hour period. For instance, if the load discharges the battery in 5 hours, the manufacturer sums up the battery power produced in that 5 hour period and calls it the battery's C5 rating. If a load of different capacity discharges the battery in 20 hours, the manufacturer sum up the power the battery produced in that 20 hour period and marks it as the battery's C20 rating. Et cetera.


A Victron Battery Charger
  • A C3 rating would mean that the manufacturer recorded that the battery was completely discharged over a period of 3 hours. Such a rating would imply a super fast discharge.

  • A C5 rating means the battery was completely discharged over a period of 5 hours. It would imply a very fast discharge.

  • A C8 rating means the battery has been completely discharged over a period of 8 hours. A C8 rating would thus imply a fast discharge.

  • A C10 rating means that the battery was completely discharged over a period of 10 hours. A C10 rating would mean that a fast discharge.

  • A C20 rating means that the battery was completely discharged over a period of 20 hours. A C20 rating would mean a medium discharge.

  • A C100 rating would mean that the battery was completely discharged over a period of 100 hours. This would mean a very slow discharge.

The reason why the C rating decreases as the number of hours increases is because of internal power losses and wastage in the battery. The C20 rate is the most common rating used in the solar industry. C100 ratings, which are used by some manufacturers, are regarded as untrustworthy and inflated.


The C Rating is one way of comparing one battery to another, especially those of the same output capacity. Also, because every appliance operates on different battery ratings, it is an important factor when choosing what battery. It is very important when considering battery choices for high performance machines that draw very high amps from the motors.


Our engineers at SolarKobo help its clients all over Nigeria make the best choice of battery in keeping with their peculiar needs and budget.

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