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ITGlossary · Batteries
C-rate
The charge or discharge current expressed as a multiple of battery capacity, e.g. 1C for a 100 Ah battery means 100 A.
Technical level:Advanced
At 1C a battery would in theory empty in one hour, at 0.5C in two hours and at 0.1C in ten. The same logic appears on datasheets as C10 or C20, meaning the capacity measured over a 10-hour or 20-hour discharge.
In a UPS the battery is often discharged within a few minutes, that is at a high C-rate. Under these conditions a lead-acid battery delivers noticeably fewer Ah than its rated value, while lithium batteries lose less capacity.
Always compare batteries at the same discharge rate. Two 100 Ah batteries, one rated at C10 and the other at C20, do not in practice have the same capacity.
Related terms
- Ampere-hour (Ah)The unit of battery capacity, showing how much current a battery can deliver and for how long, e.g. 9 Ah means 0.45 A for 20 hours.
- Battery Charging CurrentThe amount of current supplied to charge a battery, regulated by the UPS system.
- Cycle LifeThe number of charge and discharge cycles a battery withstands until its capacity falls, usually, to 80% of the original.
- Depth of Discharge (DoD)The share of a battery's capacity that has been drawn in a discharge, where 100% means fully discharged.
- Fast ChargingA charging method that restores battery capacity quickly without damage by controlling current, voltage and temperature.
- State of Charge (SoC)A battery's current charge level as a percentage of its capacity, from 0% (empty) to 100% (fully charged).