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If you are specifying a SigenStack commercial battery in the next six weeks, ask which battery controller model is on the order. That sounds like a purchasing detail. It decides whether the site can ever add a second battery.
Sigenergy issued a product release notice on 18 August 2026 for the SigenStack DC Combiner Box, model BC CMB-4, available 30 September 2026. It combines the DC outputs of up to four SigenStack Battery Controllers into one commercial and industrial hybrid inverter. Until now each controller has connected directly to its own inverter, which fixed the system at one controller-to-inverter pair. The combiner box is how a site grows storage without growing inverters.
The constraint sits in the same notice. The CMB-4 is compatible only with the new controller models, product codes 11142000 and 11142001, identified by a -BST suffix in the model name. Sigenergy states that the existing controller models are not compatible with it. From 30 September the controllers move to those new codes: 11140003 becomes 11142000, and 11140002 becomes 11142001.
Planning for storage expansion
Order a controller without the suffix today and the system works. It charges, it discharges, it backs up the site, and nothing about it looks like a mistake. The problem surfaces when someone comes back and asks for more storage.
Picture a cold store that installs storage this year sized to a single shift, then wins the contract that puts a second shift on. The natural answer is another SigenStack behind the same inverter. With a pre-suffix controller on site, that answer is not available. The options become a second hybrid inverter, or replacing a controller that is two years old and working.
This is why it is worth asking a purchasing question at design stage. The constraint attaches to the controller, not to the combiner box, so it is decided months before the expansion is even discussed.
Choosing between controller versions
If the site might expand, wait for the new codes or confirm in writing that the controller shipping to you carries the -BST suffix. If a supplier offers you clearance stock on the old codes before 30 September, that discount is buying you a closed expansion path. On a site that will never add storage it is fine. On anything with a growth case, it is not worth the saving.
If the site will not expand, the older controller is the right call and there is no reason to wait for a September product. Most single-purpose sites sit here. A workshop with a stable load and no second stage does not need a combiner box, and buying the capability for a scenario that will not happen is its own waste.
One point of flexibility is worth knowing, because it removes a constraint people assume is there. Where several SigenStack systems connect to one CMB-4, Sigenergy states the individual systems do not need identical battery capacities. A staged expansion does not have to match the size of the original installation, so the 2029 addition can be sized to the load it serves rather than to a decision made in 2026.
Installation documentation
Sigenergy puts the CMB-4 installation guide at early September 2026. That is roughly three weeks before the product is available, which is tight for anyone designing to it now.
The published figures are a maximum operating current of 180A on the controller side across four connections, 180A on the inverter side across one connection, and IP55. Communication runs on RJ45, and each controller lands on its own BAT+/BAT- DC interface. That is enough to sketch a layout. It is not enough to finalise a switchboard, a cable schedule, or the clearances an installation to AS/NZS 5139 has to satisfy, so treat any design done before the guide lands as provisional.
If you are scoping commercial storage in Western Australia, the connection is usually the longer pole than the hardware. We have written about what stalls commercial rooftop projects here. For a site where staged expansion is on the table, tell us the load and the growth case and we will specify the controller for the system you will have in five years. Get a quote and mention SigenStack.