Presumably when the seller showed OP the phone, before money had changed hands, the battery would have shown "non original" or simple "battery no good" and the

Presumably when the seller showed OP the phone, before money had changed hands, the battery would have shown "non original" or simple "battery no good" and the OP would not have bought it (or bought it for a reduced price knowing he would need to replace the battery with a genuine one)