A602/490 Sonnenschein 7 OPzV 490 GEL/VRLA Battery Sonnenschein is owned by the battery manufacturing giant Exide. With over 130 years in the battery business, Exide are known for their quality in the industry. Sonnenschein were one of the first companies to develop VRLA GEL batteries and to this...
These appear to require a special charger, not a standard or even smart charger, so I would contact these guys and inquire the best route to service and maintain this pack.