It depends on how and when you use electricity. A battery stores the solar you generate during the day so you can use it in the evening instead of buying from the grid. If your house is empty during the day and someone's home in the evening, a battery captures power you'd otherwise export for a few cent and lets you avoid buying it back at full rate later.
The alternative is to put the money into extra panels instead. The reasoning: a smaller system already has high self-consumption, surplus earns money under the Clean Export Guarantee (CEG), and a battery rarely pays for itself inside its warranty. A battery can save real money, but only if it's sized to your actual evening load and you shift charging onto a cheap night rate. With low consumption, or nobody home in the evening, you're often better off without one.
A good rule of thumb: model your own half-hourly smart-meter data before deciding. A battery that matches your usage pattern can be transformative; one bought "because everyone gets one" can sit half-empty. If budget is tight, panels-plus-export is a defensible choice and you can add a battery later if you fit a hybrid (or battery-ready) inverter now, though a battery added later doesn't get the 0% VAT rate. A €600 battery grant is expected in Budget 2027 on 6 October 2026, but it isn't confirmed and its rules aren't published yet.