I can't see any "catch" in the vendor not refunding the cost associated with their battery not being faulty.
Surely where they are not themselves in anyway at fault, but the defect lays elsewhere, its not them who should carry any cost involved?
Sorry but I really don't see why it is expected under those circumstances the vender is responsible, and it can in no way in my logic then to be described as a "catch".
Is very easy for users to abuse batteries, as reported here a user letting one drop to 6 volts!