How can I determine the charge voltage on my HyperMac battery?
As I understand


  You need to have an inverter to convert 12v DC to 110v AC in order to
  charge HyperJuice battery


is that the battery does NOT work with a 12V adapter. The battery comes with a proper charger. That text says you need an extra module ('inverter') which converts 12V back to 110V... Which can then feed the actual charger included with the original Hyperjuice battery.

That proper charger works from 90V to 240V or so, and is compatible with 'the world', as long as you can plug it in :) The 'world' has many different sockets.