Battery and inverter compatibility is treated as paperwork. A supplier sends a list, the battery model and the PCS model appear on the same line, and the pair is declared compatible. Then the system reaches a dispatch point nobody checked, the converter asks for rated power, the DC voltage has already fallen, and the current limit says no.
Compatibility is an envelope, not a list
A compatibility list answers whether two Products have been paired before. It does not answer whether the pairing holds at the operating point this project will reach. The battery supplier reports what the battery can accept, the converter supplier reports what the converter will demand, and nobody owns the arithmetic where the two meet. If the requirement is fixed and the voltage falls, the pair stops delivering rated power long before any alarm appears.
The four inputs that decide it
Three of these come from documents, not from the Products , and the fourth is the one that turns a passing calculation into a failing one. If rated output is only available above 825 V at the rack terminals, then every discharge below that point is a derated discharge, whether or not anyone wrote it down.
A worked example: eight racks against a 630 kW converter
Worked example. The project below is hypothetical, and the figures are assumptions chosen to keep the arithmetic traceable rather than measurements from a project.
The required DC power follows from the converter, not from the battery:
- Required DC power: 630 kW / 0.975 = 646 kW
- Total current: 8 racks x 100 A = 800 A
- Voltage at the converter: 884 V at the top, 734 V at the bottom, after a 16 V drop
- Available power: 884 V x 800 A x 0.975 = 689 kW at the top, 734 V x 800 A x 0.975 = 572 kW at the bottom
Figures are calculated from the assumption table above. Voltages are stated at the rack terminals and again at the converter terminals, which is where the two numbers diverge.
Nothing here is a defect. The battery stays inside its current limit, and the converter does what its datasheet says. The pair simply cannot hold rated output through the whole window, so the compatibility statement is a voltage: rated output above about 825 V at the rack terminals, derated below it. A statement without that number is not a compatibility check.
What to ask, and what is already fixed
Ask at which terminal the voltage window is specified, the rack terminals or the converter terminals, and at what temperature. Ask the supplier whether the current limit is continuous or peak and whether it applies per rack or per cluster. Ask for the point table, the protocol version and the firmware release the pair was tested on, in writing. An answer that names a product family and a protocol without a register list and a version is the beginning of a compatibility answer, not one.
The rack count, the DC voltage class, the converter model and the cable cross-section cannot be changed after the order without replacing hardware. Those four items are the envelope, so they are worth a second reading before the purchase order, not after it.
What this check does not prove
Power against voltage is one of five checks. It does not prove that the two devices agree on protection thresholds or that the DC breaker, the fuse and the pre-charge circuit are coordinated. It does not prove that the point table matches the firmware in the shipping batch, which is where most pairing failures start, as the troubleshooting sequence in sets out. It does not prove that a certificate covers the exact configuration being shipped, and it does not survive a design change that alters rack count or cable run after approval.
Ruibit runs this envelope check on requested pairs before an order is confirmed, which is why the table above is the deliverable: the crossing point, the voltage at which it occurs, and the control decision attached to it. For how the components divide that responsibility see the , for the converter side of the same question see , and for the battery paperwork see and .
The standards behind the check are IEC 62933-2-1 for system unit parameters, IEC 62477-1 and IEC 62109-1 for power conversion equipment, IEC 62619 for industrial lithium batteries, IEC 61727 and IEEE 1547 for interconnection, and UL 9540 with UL 1973 for North American listings. A compatibility statement should cite the clause it relies on, not only the designation; editions must be confirmed for the destination market and were current as of 2026-09.
FAQs
1. How do I check whether a battery and an inverter are compatible?
Walk the battery down its voltage window and calculate the power available at the bottom, not at nominal voltage. Multiply the current limit by the number of racks, subtract the cable drop, apply the converter efficiency, then compare the result with the power the converter must deliver.
2. Why can a compatible pair fail to deliver rated power?
Because the current limit stays roughly constant while the voltage falls. At the top of the window the same current produces more power than at the end of discharge. If the requirement is fixed, the shortfall appears in the lower part of every discharge, with no alarm to announce it.
3. Which number sets the worst case?
The voltage at the end of discharge, under load, at the project temperature. Nominal voltage and nameplate capacity are the two numbers most often used in a comparison and the two that decide the least.
4. Is the supplier's compatibility list enough?
No. It answers whether the two
Products
have been paired before. It does not state the voltage at which the current limit applies, whether the limit is per rack or per cluster, or which firmware release was tested.
5. What cannot be changed after the order?
The rack count, the DC voltage class, the converter model and the cable cross-section. Once these are ordered, the envelope is fixed, and no control strategy can put back the power that the voltage window removes.
