I have the dual battery setup in both 07's, it how the Police Tahoe's come from the factory. These are the parts you will need, one of each, plus a battery.
25825642 Cable
15888242 F Cable
14005061 Retainer
11509853 Screw
These parts should cost you about $116.00, it looks stock and you will should never have another battery issue.
I have schematics but you can not really see much, e-mail me at
carl@hcvind.com and I will send them to you