I sometimes charge the 12 v by putting car in park in ready mode. Usually in winter or rain. But I have a battery monitor so I know whats happening.
I don't think CCA (cold cranking amps) is a useful number for this type of vehicle. There is no cranking, as the car doesn't use a conventional starter.
My 12V battery was registering 10.5V and not charging anymore, and I was still able to start and drive the car no problem with a lithium jump pack. Of course I changed it out after a couple of starts like that.
