C-Rate Explained: How Fast a Home Battery Can Charge and Discharge
- 1C means charging or discharging a battery in one hour; 0.5C means two hours.
- A 10 kWh battery at 0.5C delivers 5 kW; at 0.25C it delivers 2.5 kW.
- Higher C-rates generate more heat and put more stress on cells.
- Home batteries are usually rated at a modest C-rate, often well below 1C.
- The inverter and the battery can each limit power, so the lower one wins.
C-rate is a simple ratio that tells you how quickly a battery is being charged or discharged compared with its size. It explains why a small battery cannot power a large load for long, and why the power figure on a datasheet is not the same as the energy figure.
What C-rate means
Battery University, an educational resource on battery science, defines C-rate as the charge or discharge current relative to capacity. A battery rated at 1C should supply its full capacity in one hour. At 0.5C, which is also written C/2, it takes two hours; at 2C, half an hour (Battery University: What is the C-rate?).
Applied to a home battery, you can think of C-rate as the power divided by the capacity. A 10 kWh battery delivering 5 kW is running at 0.5C. The same battery delivering 2.5 kW is at 0.25C.
Why power and energy are separate numbers
Capacity, measured in kWh, tells you how much energy is stored. Power, measured in kW, tells you how fast it can move. Our battery capacity guides cover the difference in detail; C-rate is the bridge between them.
A battery with a lot of capacity but a low C-rate can run the house for a long time at gentle power but cannot start a big load. A battery with a high C-rate relative to its size can deliver a large burst but will empty quickly. Neither is better in general; it depends on what you want it to do.
Good to know
A lower C-rate is not a defect. It often means gentler use of the cells. Choose the power you need for your loads, not the highest number available.
Why high C-rates cost something
The same source notes that internal losses turn some energy into heat, so faster rates shorten the effective discharge time, and capacity readings at high C-rates are lower than at low ones. It also notes that some high-performance cells tolerate rates well above 1C, while an energy-focused lithium-ion cell has protection that prevents discharge above 1C.
In practice, the cells inside home batteries are chosen for energy and longevity rather than for extreme power, so a continuous output well below 1C is typical. Pushing a battery hard, repeatedly, adds heat and stress, which adds to the ageing described in our deep dive on calendar and cycle ageing.
What this means when you compare products
Datasheets list both a continuous power and often a peak power for a short burst. Compare these against the battery's usable capacity to find the implied C-rate. If a 5 kWh battery is rated at 5 kW continuous, that is 1C; one rated at 2.5 kW is 0.5C.
Remember that the inverter has its own limit. The lower of the battery's rating and the inverter's rating sets what you actually get. A household that wants to run an electric shower, an oven and a heat pump together needs to look at the power figures, not only the kWh. For a typical home that mostly shifts evening usage, a modest C-rate is entirely sufficient.
You can try your own numbers in the home battery calculator, then compare specific models in Compare For Yourself.
Common questions
Is a higher C-rate better?
Only if you need the power. For many homes, the higher figure adds cost without a benefit. Match power to your loads and capacity to your usage.
How do I work out the C-rate from a datasheet?
Divide the continuous power in kW by the usable capacity in kWh. A 5 kW rating on a 10 kWh battery is 0.5C.
Does charging C-rate matter as well as discharging?
Yes. Charging power is often different from discharging power, and it is limited by the battery, the inverter and your supply. Check both figures.
Can a software update change my battery's power?
Makers can adjust limits in firmware, but a change must stay within what the cells and hardware allow. We could not confirm that this happens in general, so check with the maker.
Related guides
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