Choosing the correct battery for your application is paramount.
Batteries are not all the same and not all suited for every application.
If you are not connected to the utility grid, you need somewhere to store your energy.
If you are connected to the utility grid, the batteries will save enough energy to cushion you when shortages in the grid occur.
Since the panels produce energy during the day, and you may not use all the energy at the time, a stable power bank is essential to store this energy.