Real load is two numbers, and only one of them decides which of the three capacities you are allowed to buy.
Two numbers hide behind the phrase real load
The first is a daily total, in kilowatt hours. It answers how long the house runs. The second is a coincident peak, in kilowatts, measured at the moment the most appliances are running together. It answers which unit can supply that moment at all.
Most sizing conversations record the first number and estimate the second. On this product line the second one gates the purchase, because the published discharge limit rises with capacity at a fixed rate.
What the three published pages state
The published differences that decide this choice are capacity and discharge current; the third column is derived from the first two.
The published specification states these figures as of 2026-09. The right-hand column is this article's arithmetic: nominal voltage times maximum discharge current. No published page states a continuous power figure.
The discharge limit doubles with the capacity: 50 A on 100 Ah, 100 A on 200 Ah, 200 A on 400 Ah. That is the same 0.5C on all three. Ruibit publishes one discharge rate across the whole wall-mounted range, and that is what makes the peak the deciding number: each step up buys twice the energy and twice the continuous power together, so there is no step that gives you more energy without giving you more power as well.
Worked example
Assume a house with a measured daily consumption of 4.5 kWh across the outage hours it wants covered, and a measured coincident peak of 2.0 kW. For this calculation, treat the published capacity as the basis and set the inverter aside, so the battery limit is the only limit in play.
4.5 kWh fits inside the 5 kWh unit's published capacity. 2.0 kW fits inside its derived 2.56 kW. The smallest step satisfies both, so the 5 kWh unit is the answer, and the two larger units would buy capacity nobody asked for.
Changing only the daily total or only the peak forces a different model.
Case values are this article's illustration and are not product data. The forced-step column applies the published limitations in the table above.
The second row is the case that costs money without being noticed. The energy need fits the smallest unit, but the peak does not, so the purchase jumps a step and the surplus energy arrives as a side effect. The third row is the reverse: the power was already sufficient and the capacity was not.
What the answer is sensitive to
Adding nameplate ratings is the most common error. A 3.6 kW oven, a 2.5 kW air conditioner and a 1 kW well pump do not draw 7.1 kW at the battery; the battery sees what genuinely runs at the same moment, after the inverter. If the peak was built by adding labels, the choice moves up a step on paper only.
The battery limit is also not the system limit. These are battery-side figures, and the inverter has its own limit that can bind first, so the effective ceiling is whichever is lower.
Temperature and duration matter and are not published. No page in this range attaches a temperature or a duration to any discharge limit, so whether a limit holds for the seconds a compressor needs cannot be read from the pages.
The physical and certification steps move with the capacity too. The published footprints go from 650 x 520 x 180 mm and about 55 kg, to 650 x 720 x 220 mm and about 95 kg, to 750 x 1000 x 280 mm and about 180 kg, so a choice driven by peak load can land on a unit the original wall position was not scoped for. The certification lists differ as well: the 5 kWh page lists CE, UN38.3 and IEC62619, while the 10 kWh and 20 kWh pages add UL1973. Stepping up changes what the model is documented for, not only how much it stores.
Where the published pages stop
No published page in this range states a usable energy figure. Capacity is given at 51.2 V, and cycle life as 6000+ cycles at 80 percent depth of discharge, which is the basis of that test rather than a usable capacity to divide into a run time. The arithmetic above compares the three models on the same basis; it does not produce a run time the house will see.
Nor does any page state that the battery-side current limit equals the system limit.
What to confirm before ordering
Ask for the energy figure the run time was calculated on and its basis, meaning the depth of discharge and whether it is measured on the DC or the AC side. An answer that returns the nameplate capacity to a question about household run time is a number that cannot be used.
Ask whether the published maximum discharge current holds at the temperature and for the duration your peak requires. An answer that repeats the specification without a duration has not answered the question.
Ask for the certificate scope of the exact model quoted. An answer that names a certificate covering the family, when the 5 kWh page does not list UL1973, is a scope gap rather than a confirmation.
Two items cannot be changed once the order is placed. The capacity step is one: moving up later means a second unit and a second wall position rather than an adjustment. The certification scope is the other, because it follows the model page rather than the installation.
At handover, record the measured coincident peak and the daily energy total the choice was made on, the usable-energy basis any run time was calculated from, and the certificate scope of the model as delivered. Those three lines are the benchmark for any later run-time complaint or market-approval review.
Treat this as sizing judgment: only the first table is a published requirement, and the quotation should keep the two separate.
FAQs
1. How do I decide between 5kWh, 10kWh and 20kWh?
Measure two numbers first. The daily energy total in kWh decides whether the smallest capacity is enough for the outage hours you want covered. The coincident peak in kW decides which unit is allowed to supply that moment. A house can have enough daily energy for the 5 kWh unit and still be forced to the 10 kWh unit because the published discharge limit of the smaller unit is lower.
2. Why does a larger capacity give more power as well as more energy?
The published pages carry the same 0.5C discharge rate on all three: 50 A on 100 Ah, 100 A on 200 Ah, 200 A on 400 Ah. Each step up therefore doubles the energy and the continuous power together, so there is no step that adds storage without adding power.
3. Do the published discharge currents mean that current is available at the terminals?
They are battery-side figures, and the inverter has its own limit that can bind first, so the effective ceiling is whichever is lower. No page in this range attaches a temperature or a duration to any discharge limit, so a limit for a compressor start cannot be confirmed from the published data alone.
4. Is UL1973 listed on all three models?
No. The 5 kWh page lists CE, UN38.3 and IEC62619. The 10 kWh and 20 kWh pages add UL1973, so stepping up changes the documented scope of the model.
5. What should be confirmed before ordering?
The usable energy figure any run time was calculated on and its basis, the temperature and duration behind the discharge limit, and the certificate scope of the exact model quoted.
