The plate on the battery unit says 25.6V 280Ah *6 = 51.2V 840Ah so there are 6 batteries inside. The sum shows that there must be 3 blocks of two in series which are then wired in parallel together. The advantage of batteries in parallel is that you add the storage in Ah. They are connected in series pairs first because that doubles the voltage without affecting the Ah. Problems arise if the batteries have different voltage ratings. Then one battery can discharge through another. This is known as cross-discharge. Diodes can be used to prevent it.
