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C Rating

C Rating

The C rating of a standby battery  describes the rate at which the battery is charged or discharged, expressed as a multiple of its rated capacity in amp-hours (Ah).

C rating = Current (A) Capacity (Ah)

For example;

  • 1C discharge rate means the battery will deliver its full capacity in one hour; or
  • 0.5C over two hours; or
  • 2C in 30 minutes.

This rating is commonly applied to standby batteries in fire protection systems—such as those supporting fire panels, and emergency warning systems, where low, continuous discharge rates are typical.

Conversely, the related term P-rate is based on power output (watts) rather than current. While less commonly used in fire safety, it may still be relevant when assessing system power requirements or inverter sizing. In simple terms: C-rate reflects current draw; P-rate reflects power demand.

    Disclaimer

    In preparing this definition, we have drawn from various sources including Legislation, Codes, Standards and industry information, research and knowledge.  Like the english language, these definitions may subtly change from time to time. As such these definitions are provided solely on the basis that users will be responsible for making their own assessment of the definition and and are advised to verify all relevant representations, statements and information.