Also, what you can do is get a cigarette lighter plug with a cord, and splice on the barrel plug attachment of the right size, and charge it through your cigarette lighter port in your vehicle, as long as the engine is running.
If you do end up buying a replacement AC wall wart for charging it, keep in mind that the wall wart can severely overcharge the battery, if left plugged in continuously.
It is simply a poorly regulated power supply that will have about 16 volts across your battery by the time it is charged, destroying it.
I wouldn't leave it plugged in for more than 10 hours.
Finally, if you have a plug in car battery charger at home, you can simply clamp the jumper leads of the pack onto the car battery charger's clamps, and then switch the pack on, and it will charge that way.