Do I have to absolve the battery seller, who replaced it for me under warranty without asking about the cause of the malfunction, knowing that the cause of the malfunction might have been my own negligence?

As long as the warranty card grants the customer the right to replace the battery if it malfunctions before the end of the warranty period, there is no harm in benefiting from the new battery. The guarantor can inspect the battery to determine the cause of the defect. If the guarantor agrees to provide the battery without inspection, and there is no deception or fraud on the part of the customer, then there is no harm in that. It is permissible to specify a period for guaranteeing manufacturing defects or to undertake maintenance for a certain period agreed upon by both parties or customary.