C discharge

P Peter Lu Energy Storage Product Manager, GreenMore The discharge rate, usually written as a C-rate, tells you how fast a battery can deliver its stored energy. It is the link between the capacity of the battery in kWh and the power it can actually put out in kW. Pick the wrong C-rate for your loads and the system either cannot start your heaviest appliance or you have paid for power capability you will never use. What a C-rate actually means A 1C discharge means the battery delivers its full rated capacity in one hour. A 0.5C discharge takes two hours. A 2C discharge takes half an hour. The conversion to power is straightforward: power equals capacity multiplied by the C-rate. Power (kW) = Capacity (kWh) × C-rate 10 kWh × 1C = 10 kW 10 kWh × 0.5C = 5 kW 10 kWh × 2C = 20 kW The C-rate is a rate, not a guarantee. A battery that can sustain 1C for an hour may not be able to sustain 2C for half an hour without the voltage sagging or the cells heating beyond their safe range. The continuous and surge ratings in the datasheet are the numbers that matter. Why C-rate matters for a home or commercial system Two systems with the same kWh capacity can behave very differently if their C-rates differ. A 10 kWh home battery rated at 0.5C delivers about 5 kW of continuous power, enough for lighting, refrigeration and a small heat pump running together, but not for an electric oven, a clothes dryer and an air conditioner at the same time. The same 10 kWh capacity rated at 1C can deliver about 10 kW and cover those heavier loads. In commercial systems the C-rate determines whether the battery can follow a fast frequency signal or only smooth out a slow peak. This is also why sizing a system only by kWh is incomplete. You need to size by both kWh (how long) and kW (how much at once), and the C-rate is the link between them. Typical C-rate ranges by application Application Typical continuous C-rate Why Home storage, evening self-consumption 0.2C to 0.5C Long, steady discharge over several hours Home backup with mixed loads 0.5C to 1C Must cover a range of appliances and inductive starts Commercial peak shaving 0.5C to 1C Sustained high power over a demand window Fast frequency response 1C and above, short bursts Sub-second to minute-scale power swings These are realistic ranges, not fixed rules. The exact value for a specific project depends on the inverter rating, the load profile and the thermal design of the battery. Read the continuous and surge ratings in the product datasheet rather than relying on a single C-rate figure quoted in marketing. Energy storage battery cycle life and capacity retention Is a higher C-rate always better? No. A higher C-rate means the battery can deliver more power for a shorter time, but it also brings trade-offs. High-rate cells generate more heat for the same energy moved, which shortens life if the cooling is not designed for it. High-rate designs cost more per kWh because they use thicker current collectors, lower internal resistance materials and more aggressive thermal management. If your loads never exceed 0.5C, paying for a 2C battery is wasted money that also runs hotter than it needs to. The right C-rate is the one that covers your actual peak load with some margin, not the highest number on a brochure. For a home, start from the sum of the loads you want to run together, add the inductive start surge of the largest motor, and choose a system whose continuous and surge ratings exceed that number. Continuous versus surge rating Datasheets usually list two power numbers: continuous and surge (sometimes called peak). The continuous rating is what the system can sustain without overheating. The surge rating is a short-time capability, typically for a few seconds, used to start inductive loads like compressors and pumps. A system that meets your continuous requirement but not your surge requirement will trip when the compressor starts; one that meets surge but not continuous will overheat under a sustained load. Check both. How to match C-rate to your loads List the appliances you want the battery to support together and add their running watts. Add the starting surge of the largest inductive load (often 2 to 5 times its running watts for a compressor). Choose a system whose continuous rating covers the running total and whose surge rating covers the starting surge. Confirm the inverter's output rating matches; the battery cannot deliver more power than the inverter can convert. Check the datasheet for the temperature range and derating curve. A battery rated at 1C at 25℃ may be limited to a lower C-rate at 40℃ or below 0℃. You can see our residential systems on the home energy storage system product page and the commercial range on the commercial energy storage category page. If you share your load list and target autonomy, we can confirm the continuous and surge ratings that fit — use the contact page. FAQ What does "1C" mean on a battery spec? It means the battery can deliver its full rated capacity in one hour. A 10 kWh battery at 1C outputs about 10 kW for one hour. The actual continuous and surge ratings on the datasheet define what is sustainable in real use. Why does my 10 kWh battery only power about 5 kW of loads? Most home LiFePO4 systems are rated around 0.5C continuous, so a 10 kWh unit delivers about 5 kW. That is a design choice: it favors longer runtime over short bursts. If you need more power from the same capacity, look for a system rated closer to 1C, or add modules in parallel where the design allows. Does a higher C-rate reduce battery life? Sustained high-rate discharge generates more heat, and heat is the main driver of cell aging. A system designed for 1C continuous with adequate thermal management will handle it; the same cells run hard without the cooling will age faster. Follow the datasheet's rated continuous C-rate and temperature limits. Can I increase C-rate by adding more modules? Adding modules in parallel increases both capacity and total power, so the system C-rate relative to the new capacity can stay the same while the absolute power grows. Check the manufacturer's stated maximum parallel count and that the inverter can accept the higher power. P Written by Peter Lu — Energy Storage Product Manager, GreenMore Peter works with distributors, installers and system integrators to size residential and commercial storage around real load profiles. He focuses on LiFePO4 systems that match the inverter, grid rules and backup needs of each destination market.