We managed to get our hands on the manufacturer's datasheet, which shows a range of data, including the battery life: https://asset.conrad.com/media10/add/160267/c1/-/gl/000250818DS01/fiche-technique-250818-batterie-au-plomb-yuasa-np12-12-12-v-12-ah-plomb-agm-l-x-h-x-p-151-x-98-x-98-mm-cosses-plates-635-mm-sans-entretien.pdf