Why are batteries connected in series/parallel?
With a series/parallel connection 2 x 2 batteries are first connected in series.Then these 2 groups are connected in parallel.
4 batteries of 12V / 120Ah become a system of 24V / 240Ah.
A very important but often forgotten part in a series/parallel connection is the so-called compensation cable.
This cable, mounted between the series strings, takes care of voltage differences over both strings by equalisation. In an ideal situation, with 100% identical batteries, this cable is currentless.