Single big battery v/s 2 batteries in parallel

Matt, interesting explanation based on some extreme limits.

I agree there will be some circulating currents and some ampacity lost, but it is typically minimal when using batteries of the same type, age, and physical condition.

If battery technologies are mixed, or batteries of differing ages and physical conditions exist, then your extreme limit examples can occur.

In general, and if standard practices are followed, batteries can be connected in parallel without issue.