Behold....the
Duo-Pack-01 Turbo Express battery pack:
And here it is installed, fits like stock door.
You can see the internal charging port on the first photo, and there is a quick disconnect that can allow it to be removed from the Turbo Express.
Also another benefit of the mod is weight reduction, just weighed 6 AA batteries - came in at 5.2 ounces, the new lithium ion pack weighs 3.5. Unit doesn't feel weightless now, but you can tell the difference.