I second all the votes for a new battery. The factory batteries are good for about 3 years.
If you have the budget, spend a little more and get an AGM battery. In the US, I got mine from Autozone. They will check your battery and charging system for free.
You’re right about the CX-5. Strike it from the list, it is too small for car seats.
https://www.reddit.com/r/CX5/search/?q=car seats&restrict\_sr=1