You mentioned needing 24v to power this thing.
If that is correct, direct your favorite search engine to look for a size 'A23 battery'. I believe they are made from a stack of button cell batteries.
It is about half the size of a AAA and runs 12v, so two would give you the required 24v and be no larger than a AAA.
Attached image A23* battery on a CD with a standard 9v.
*(Duracell calls it the MN21/23)