After a short discussion I managed to convince him about battery life is longer than one year regardless of who manufactured it.
I was interested in what caused the previous batteries to fail so I asked the owner to visit us with his motorcycle. I wanted to check the starter system, the starter motor mechanism and the alternator regulator charging function.
As he told me, he bought his motorcycle 5 years ago. Immediately in the first season, the starter motor’s starter clutch had to be replaced. Then he was later notified front brake recall campaign. No other problem occured.