Makie doll with expressive animal ears

Katsideswide has modded her alpha-version Makie doll with a pair of expressive animal ears. She drilled holes in the head of her custom, 3D printed dolls, used the head-cavity to house a controller, and went to town.

Ok, i've just started tinkering around with some tiny servos to get Suekat expressing herself. I'm yet to get the drill out to perform amateur surgery on her skullcap but I'm hoping the results will be exciting! I don't want to promise anything yet but I've hooked up an arduino pro mini, and the conveniently sized head cavity means I think i can get a fair amount in there. It looks like there's a handy hole in the neck leading to what looks suspiciously like a space for a battery in Suekat's back. Unfortunately I can't get a standard 9V battery into the space! It's a fraction too small. I was wondering what battery it was designed for? And if there's any chance I can get 9V out of it?

Batteries?

(Disclosure: I'm proud to say that my wife co-founded MakieLab, manufacturers of the Makie dolls)