This is a 15v compatible model genuine quality power adapter which delivers continuous fixed 15v dc power output, it can be used to safely charge the battery in your jump starter. We recommend using a 14/15v adapter to charger the 12v battery. Charging should be higher voltage than the 12v battery, for example car 12V batteries charge at 13.8V so ideally to charge your battery you need a 14V/ 15V dc power adapter. Leaving the charger on any longer than 10 hours can damage the battery, so we recommend a 9-10 hour charge time but always keep a check that the battery doesn’t overheat. The original adapter that was supplied with your jump starter maybe 12v 1.5amp but its likely to be the old style heavy unregulated chargers, that usually deliver alot higher voltage than 12v to the battery.