I usually use an extension cord running into the back yard - but then I'm powering the mount, dew heater, camera, laptop, powered USB hub, and lightbox!
For portability I use
this which works fine: it has 2 1v DC cigarette-lighter type sockets and also an inverter that means I can run AC if I need to.
Meade makes a plug that powers the mount from a 12v DC cigarette-lighter source. You can get a transformer that will plug in to household AC and convert to 12v DC from Jaycar, Dick Smiths, Bintel ...