Quick Answer: BESS certifications are mandatory safety approvals for Battery Energy Storage Systems. You need UL 9540 for the USA, CE Marking for Europe, IEC 62619 globally, and BIS IS 17855 for India.
We usually measure or convert the watts into amps of solar panels to figure out how much current (amps) is being stored in the battery. Or we measure the amperage of the solar panel output to select the wire sizefrom solar panels to.