[Boatanchors] Adding DC source to Kenwood TKR720/820

[HL1FB]

Hello;
     I recently got a Kenwood TKR720  and reprogrammed to ham band. I would like to add battery power source to it.
I heard Kenwood had an option to add DC source. Anybody knows to add/modify the radio
for DC source??
de HL1FB/WW6N