Ok. Good luck drawing 200 amps for hje heat pump from a standard 70-100ah lead acid starter battery for more than a few seconds.
It would be tha eqvivalent of driving your gas car on the starter engine.
I guess you would go through a lot of trouble, and a lot of expensive big atea wiring...
Dude no.
It does not work like that. You need to read up.
You need about 2-6 kW to generate any kind of cabin heat. That is about eqvivalent of what the car i drawing out of the traction battery for driving on flat.
The 12V keeps interior instruments and light on. Thats about it.
Get a bigger...
Dont listen to the Naysayers. I think this is an awesome idea, and i would like to try it out myself as i have just swapped my old gen1 63% SOC pck forva fresh one.
This has been done on a large scale in a massive battery park in California, but to do it "Down and dirty" DIY i guess one would...