Is there a way to install a new 12v battery, - so not have any 'issues' with the blend doors or having to re-program other things

 

Yes, just do it. Disconnect the Neg - first, then Pos. +. When the new one is in place, connect the Pos. + first and then the Neg. -.

Then leave it alone so it can reset all those things BEFORE you attempt to start it or use other accessories. I have never reprogrammed anything after changing an H3 Battery.

 

12v connected to auxiliary-cig lighter socket- OBDII port or battery cables.