Ask three installers what a 10 kWh battery can back up and two of them will answer in hours without looking at the load. The question cannot be answered in one unit, because a home battery carries two. Kilowatt-hours say how much energy is stored. Kilowatts say how fast that energy can come out of the terminals.
The belief that shortens quotations
The common belief is that the kilowatt-hour figure is the whole specification. Ten kilowatt-hours, ten hours of backup. It arrives in the quotation as a single number, and it survives to the order because nothing in the sales conversation contradicts it.
Where it breaks
It breaks on the first load that draws more than the battery can deliver, and on the first winter outage that lasts longer than the stored energy allows. Those are two different failures, and they have two different fixes.
A battery can hold enough energy for the whole night and still refuse to run the load in front of it. The published figures for this range show the two numbers moving separately. The HZEB-LCT-10 publishes a capacity of 10 kWh beside a maximum discharge current of 100 A at a nominal 51.2 V, which is an arithmetic ceiling of about 5.12 kW of continuous output. The HZEB-LCT-20 publishes 200 A at the same nominal voltage, about 10.24 kW. Energy doubled and power doubled, but that is a design decision in this range rather than a rule, and the two figures have to be read separately on every unit.
Two quantities, two questions
The capacity values and the surge figure are quoted from the published product specifications. The continuous kilowatt column is arithmetic on the published voltage and current, not a tested figure. Verified as of 2026-09.
One row of that table is arithmetic and the other two are published, and the distinction matters when a quotation is defended later. Ruibit publishes the voltage and the current limit on the product pages, which is what makes the continuous power ceiling calculable before a quotation is written. The usable energy under a proposed reserve setting is not published and has to be requested, because it depends on a configuration choice rather than on the product.
Published records treat them as two decisions
The project records published for this range show the two numbers being settled separately rather than derived from one another. The Tanzania residential record lists a battery capacity of 16 kWh beside an inverter power of 10 kW, so the record itself separates storage from conversion. The Kenya commercial record lists 64 kWh against a 50 kW three-phase inverter, and states that the 64 kWh size was chosen to balance high discharge rates against cost-effective storage, which is the same trade-off described from the other direction. Two records, two ratios, and neither figure can be inferred from the other.
How much do you need
Work out the power question first, because it has a hard limit, and the energy question second, because it has a soft one.
Worked example. A household backs up a fridge, the lighting, a router and a well pump. Suppose the circuits that stay on draw 0.5 kW continuously, and the pump draws 1.2 kW while running but needs about 4 kW to start. The coincident peak is roughly 4.5 kW for as long as the start lasts, and it is the number the equipment has to survive. A unit limited to 5.12 kW can serve it. A unit limited to 3 kW cannot, however much energy it stores.
The energy side then follows from the duration. Six hours at an average 0.9 kW is 5.4 kWh of AC demand. At an illustrative 92 percent conversion efficiency that needs about 5.9 kWh of DC discharge, and a reserve setting of 20 percent takes the required nameplate capacity to roughly 7.3 kWh. Both assumptions are stated here rather than published, and they change the answer, which is why the assumptions belong in the quotation.
If the coincident peak exceeds the published discharge limit of the chosen unit, the answer is to move up the range or to shed a load, and it is not to add storage.
Keep the two failure modes apart when sizing, because neither number fixes the other's problem. Adding battery modules raises the energy that can be stored and does not raise the current the unit can deliver. Selecting a larger inverter raises the power available at the terminals and does not add a single kilowatt-hour of storage.
What to ask, and what to record
Two requests belong in writing before the order. Ask the supplier for the continuous kilowatt rating at the intended operating temperature, and for how long the unit can sustain output above it, because a short surge figure and a continuous rating are different numbers that are often quoted as one. Ask for the usable capacity in kilowatt-hours under the proposed reserve setting, because nameplate capacity and usable capacity are not on the same basis.
Two items are effectively irreversible once the job starts. The partition of the distribution board decides which circuits survive an outage for the life of the installation, and the position of the inverter and the battery is fixed when the wall is opened. Both are cheap to change in the proposal and expensive afterwards.
At handover, record both numbers rather than one: the coincident peak in kilowatts that the design was checked against, and the usable energy in kilowatt-hours it was sized to. Add the load list and the reserve setting beside them. If the household later adds a large appliance, that record is what shows whether the system was undersized from the start or simply asked to do something new.
A quotation that states only kilowatt-hours has described a fuel tank. A quotation that states only kilowatts has described a hose. A home needs both, and the load list is the document that decides each one.
FAQs
1. What is the difference between kW and kWh in a home battery?
Kilowatt-hours measure stored energy and answer how long the system can run. Kilowatts measure power and answer what can run at the same time. A battery is specified with both, and the two figures are read separately on every unit.
2. Why is a 10 kWh battery not 10 hours of backup?
Because backup time is usable energy divided by the average load, and the load is not fixed. A 10 kWh pack supplies less than 10 kWh of AC energy once depth of discharge, reserve settings and conversion losses are accounted for. Ten hours only holds if the average load is around 1 kW after those deductions.
3. Which number should I size first, kW or kWh?
Size the power figure first, because it has a hard limit. Check the coincident peak, including the starting power of any motor-driven unit, against the continuous rating of the chosen unit. Then divide the usable energy by the average running load to get the hours.
4. Can more battery capacity fix a power shortfall?
No. Adding modules raises the energy that can be stored and does not raise the current the unit can deliver. If the coincident peak exceeds the published discharge limit, the options are to move up the range or to shed a load during the outage.
5. What should the quotation state?
The continuous kilowatt rating at the intended operating temperature, how long the unit can sustain output above it, and the usable capacity in kilowatt-hours under the proposed reserve setting. Add the load list and the coincident peak the design was checked against, so a later appliance can be assessed against the same basis.
