Charge Rate

What is charge rate?

Charge Rate is the amount of energy added to a battery over a given unit of time. Often measured in Amps.

Key Takeaways:

• Charge rate is the rate at which a battery charges over a given unit of time.
• Charge rate is denoted by the C-rate which indicates the number of hours required to fully charge or discharge.
• C10 batteries are recommended for most solar applications.

Understanding charge rate

Charge rate is the amount of energy added to a battery over a given unit of time. This is measured by a unit called the C-rate which indicates how quickly a battery charges or discharges relative to its maximum capacity. The C-rate is defined as the charge or discharge current divided by the battery’s capacity to store an electrical charge. This is typically abbreviated as ‘C’ with a number to indicate how many hours it will take to fully discharge under standard usage.

For instance, a battery with a rate of C1 would fully charge or discharge in one hour. This is never expressed as a negative number, so whether this is describing charging or discharging is entirely dependent on the context.

Example: When the 100 kWh battery in a Tesla Model S P100D is undergoing supercharging at 120 kW the C-rate is 1.2C and when that battery delivers its maximum power of 451 kW, its C-rate is 4.51C.

For solar applications C10 batteries are recommended.

Related Terms

Battery – A storage device for electrical energy, typically in a chemical solution, that can be used as a source of power.

Discharge Rate – The amount of energy removed from a battery over a given unit of time. Often measured in Amp-hrs.

Battery Cycle Life – The typical number of charge and discharge cycles that a battery can undergo before it reaches the end of its useful life.