QUESTION SOLAR PANEL AND POWER

[brian25]

how to know if my backup storage is already in full charge lets say if i have this batteries
and i use this panel 80W.

 

[Hero999]

Measure the battery voltage.

Your drawing doesn't show how the batteries are connected or the solar cell voltage. The battery voltage could be 12V, 24V, 36V or 60V, depending on how they are connected.