Why are there single quotes around the numbers?
Is "mySwitches" a number or a string?
Perhaps the UNO compiler parses the single quotes differently than the Tiny compiler.

I realize this is an old post and you have probably solved your problem already but the DUAL MOTOR TINYSHIELD (ASD2302-R) says it supports up to 11 volts.

You could just solder female headers into the proto-board. (assuming you don't want to use the terminal block board)

Sounds like a good idea, but I think stacking batteries that aren't factory matched might be a problem.

I don't see why you couldn't solder the male and female connectors back to back...

I like that idea. Either two connectors or possibly an IDC connector for more heavy duty ribbon cable. Could make a bracelet.
I wonder whether IDC Hirose connectors are available. Then adapter boards wouldn't be required at all.