Batteries and Safety question

So, I’m researching building a tracked robot in the 1k price range.

I’m finding most motors I want are 36-52V, 36A draw range. I’m hunting batteries, and trying to figure out what’s safe to put in series, and what I can mix and match.

Is it safe to:
* put 12v car batteries in series until I reach 48v?
* put 6s lipo batteries in series until I reach 48v?
* put 12v car batteries and Lipo batteries together in series until I reach 48v?

Ideally, I want to use a 6s lipo + a 12v lead-acid AGM battery together, and just wire them together.

However, I want to not start fires, explosions….

Thanks!