There is a 3rd-party vendor for an internal PSU for DQ77KB and other thin-miniITX boards.
Vendor: HuntKey http://www.huntkeydiy.com/en/about.html
Model no.: HKF1501-3A
Desc: 150W internal PSU (19V/7.9A)
The 2-pin internal Molex connector still requires 19V DC, same as the external DC jack. Pin 1 (near the lock) is 19V DC and the other is ground.
As far as connectors go, half of a standard 2x2 CPU cable connector would work as long as it provides the 19V DC. (FYI, 2x2 CPU output from a standard ATX PSU is only 12V DC).
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This website has a module that convert input from a battery of one voltage to a battery of another voltage. So you could use some kind of other batteries or build your own LION Battery Pack from say a rechargable batter for an electric bicycle or something like that.