Adding a battery to panels you already have, or fitting both at once? The way the battery connects decides how much work the install needs.
An AC-coupled battery has its own inverter and connects to your home's mains wiring, so it can be added to existing panels without touching the solar inverter. A DC-coupled battery shares a hybrid inverter with the panels, so solar can charge it without an extra conversion. AC suits retrofits; DC suits new installs or an inverter replacement.