help

So i returned my Thinkpad X1 Carbon G9 to a seller, whom I bought the laptop from refurbished. It stopped taking charge within 12 hours of unboxing, and i shipped it back. They told me the laptop didn't receive charge because it was due to the "CMOS battery", but the google searches show it was highly unlikely it was caused by CMOS; it's either battery or charging port.

Laptop experts, are they telling the truth?