I'll give my 2c in here now, based on how this thread is going.
You posted a "from the heart" post earlier, explaining issues, and I guess expecting people to forgive you, or understand the troubles, and have some good faith that it might be sorted. That, in my eyes, was the hard part. You've already admitted the problem, and identified how to proceed to fix it and get SSS back up and running.
So why the difficult attitude now, mate? I've met you, during COVID (not sure if you remember), you bought beer kits from me. We had a lekker chat. I got the idea you were a decent, honest, family man. Things go wrong. Things went wrong for me for a while as well. I understand.
But don't let pride or arrogance or plain simple pigheadedness cause so much damage to your image that it cannot be redeemed. As I said, the hardest part is done. Apologize to the bloke, get him his replacement battery, take back the old one and amend the issue. Even if you don't get his approval - who cares? Your business does not depend on one man.
If it turns out his battery is not faulty and he's taking you for a sucker - that's another story. He has a profile on Carbonite and I'll personally help you gather all the info you need to take it further if he is indeed scamming you (which I doubt). If there's something wrong with his battery, he's merely getting what he paid for - which is fair and right, no?
That's my 2c. Take it or leave it.