The retrofit question is often about control architecture
A hybrid inverter can combine PV conversion and battery control in one platform, while an AC-coupled retrofit generally adds a separate battery inverter alongside the existing solar inverter. Either architecture can work well, but the control path, metering requirements and backup design are different. The starting point is the equipment already installed: inverter model, remaining warranty, array voltage/current, export controls and whether the existing inverter must be retained.
Replacing the solar inverter can simplify some functions but adds scope
Moving to a compatible hybrid inverter may create a more integrated solar-and-storage system with fewer conversion stages during direct PV-to-battery charging. It can also mean re-engineering strings, protection, monitoring and grid settings that were already working. Before replacing equipment, compare the actual compatibility list and the cost of touching the existing PV system. The battery-inverter compatibility guide is a useful evidence checklist.
AC coupling can preserve the existing PV investment
A separate AC-coupled battery can often leave the existing solar inverter and array largely intact. That can be attractive when the solar system is recent or difficult to reconfigure. The trade-off is an additional conversion path and a need for correct site metering so the battery knows when the property is importing, exporting or producing. Backup capability also depends on the battery system gateway or transfer equipment; AC coupling by itself does not guarantee whole-home backup.
Choose on system fit rather than architecture slogans
Compare usable battery capacity, charge/discharge power, backup power, meter/CT requirements, export-limit behavior, warranty interaction and expansion options for the exact products. A hybrid design is not automatically more efficient in every operating condition, and AC coupling is not automatically easier on every site. Use the existing-solar retrofit comparison alongside a site-specific quote so duplicated scope and hidden compatibility work are visible before purchase.