Three questions, not one
Battery proposals often collapse three separate quantities into “backup”: usable energy in kilowatt-hours, available power in kilowatts and the circuits physically connected to the backed-up side. Energy influences duration. Power and surge behaviour determine what can run at once. The switchboard and transfer architecture decide what is energised at all.
Use the essential-load schedule to document continuous demand and daily energy, then check the exact battery, inverter and transfer-equipment limits in current product documentation. The worksheet is an estimate and does not replace the licensed design.
Common architectures
Selected-circuit backup moves nominated circuits to an essential-load section. Whole-home backup places a broader installation behind compatible transfer equipment but still remains constrained by system power and load behaviour. Managed-load backup can shed or sequence circuits through supported controllers. The labels are not interchangeable, and product families support different configurations.
Tesla describes its Backup Gateway as the component that detects grid outages, disconnects the backed-up system from the grid and acts as a site meter. Enphase identifies its System Controller as part of supported backup configurations and publishes separate installation and commissioning material. Those product documents—not a generic diagram—govern the actual arrangement.
Select essential loads from evidence
Start with what the customer needs during a realistic outage: refrigeration, lighting, communications, medical or work-critical equipment and limited general power. Record continuous demand, expected run-time, starting behaviour and whether any load can be deferred. Large thermal and motor loads can consume the available power quickly or create starting conditions that a simple daily-energy total misses.
Do not imply that a circuit is backed up until its connection and operation have been verified. The handover should name backed-up and non-backed-up circuits, operating limitations, reserve behaviour and the controls available to the owner.
Commission the outage behaviour
A useful record captures the system state before the test, the transfer event, which circuits remained available, any load shedding, battery power and state of charge, alerts, restoration and return to normal grid operation. Testing, switching and switchboard work are licensed-worker tasks and must follow the exact manufacturer process and applicable Australian requirements.
AS/NZS 5139 covers safety and installation requirements for battery systems used with power conversion equipment. AS/NZS 4777.1:2024 covers installation requirements for inverter energy systems and distinguishes its scope from PV-array and battery-system standards. Always work from the current editions and the approved design.