@Eric Echard, are you sure it's the battery that's stopped charging? Have you checked the voltage output of the charger to see if it's still working? That would be my first suggestion and then take a look for an external fuse on the battery that might be blown. Another possibility and a fairly common problem is a broken connection at the charger port, just inside the battery. You would want to contact Leisger/Magnum Bikes in the US at 323-375-2666 for help with this or to determine if that battery really needs replacement.
Leisger's a fairly new brand in the US, so I'm thinking that it would be odd that the battery is already dead. However, if you left the battery uncharged in storage for a long time, say 6+ months, it may have gone into a sleep mode where the battery voltage has dropped to the point that the Battery Management System thinks there's a problem and won't accept a charge. If that's the case, it is potentially possible to restore the battery but it's a risky process.