Energy and power answer different questions
A battery stores energy, commonly expressed in kWh. Available power in kW describes the load it can support at a particular moment. High energy capacity does not guarantee that a pump will start: the battery, inverter and their connections each impose limits. Selection therefore needs a consumption schedule, starting requirements and the intended period without charging as separate inputs.
Nominal capacity is not the usable reserve
A retained state-of-charge margin, conversion losses and the system's own consumption reduce runtime. Temperature and ageing may also affect available capacity and power. Compare offers using the same charge window and test conditions. A cycle-life number without depth of discharge, temperature and an end-of-life capacity criterion gives little basis for estimating service life in your use pattern.
Check the complete combination
Battery management must cooperate with the inverter, charging settings and protection. Being physically connectable is not proof of compatibility. Assess the installation location against the manufacturer's temperature, access and environmental requirements. Future expansion depends on permitted configurations; adding modules arbitrarily can create a combination that has not been supported or assessed by the supplier.
Include the next recharge
A reserve sized for one interruption does not describe repeated outages. After discharge, the charging source must serve ongoing household demand and restore stored energy within the available time. For solar charging, examine the difficult season rather than annual yield alone. Use the autonomy calculator to compare scenarios, then provide the electrical designer with critical loads and likely intervals between outages. That information is more useful than choosing a battery size without a recovery plan.