Still using chunky ass D batteries for your portable? Fuck all that shit.
With this adapter, you can now power your portable with any common power bank that you would charge your phone with. Waaay preferable to dealing with batteries. And this way, your cutting time will only be limited by the capacity of your power bank (and those things hold quite a lot of juice). Very important: make sure you buy the USB 5V to 12V version in particular. You can buy this adapter here.
P.S. I should specify that I use this with my Numark PT-01. Not sure about using it with the Vestax or others.