@ajb2k3, @watson Thank you so much.
Uuum, stacking is very convenient but considering batteries is not convenient.

Oh! I see.

Another similar question:
I have a M5Stack-Basic. So I want to stack a Battery Module with it.
But this is not good according to the CAUTION. Is this right?

Can I stack if I remove the battery included in the Bottom?

Can I stack a Battery Module and a PLUS Unit at the same time?
I am worried because I looked at the caution in the document of Battery Module showing below.

CAUTION: Do not use this battery module at the same time as other batteries (such as the M5 Core bottom battery). At the same time, in the worst case, there is a danger of catching fire.