Fraud is illegal in any sale or transaction or contract, whether between a company and a consumer or a person to person transaction. It's also illegal whether it was an in-person transaction or one done over the Internet. Fraud is the intentional or knowing misprepresentation (or lie) of a material (or important) fact, made to induce (or convince) the other party to enter into a transaction, where it was reasonable for the other party to rely on that false representation. If the criteria for fraud are met by the circumstances of this sale, you'd have a right to rescind the sale, return the battery, and get your money back. Whether or not suing the other party, if they don't voluntarily agree to rescind the transaction, would be economically worthwhile is a different matter, obviously--sometimes you have rights, but it's too expensive to enforce them.