The Energizer A23 is about the cheapest battery on the rack. Some places you can get 2 for less than 3 bucks.
http://data.energizer.com/PDFs/A23.pdf12V - shouldn't be a problem for the circuit.
The trick is to fatten and lengthen the battery.
I used some vinyl washers, bibb screws and shrink wrap.
These are old fashioned faucet washers - you can get them at any big home store or your local hardware store.
I used 4 washers per battery. 2 beveled and 2 flat...One beveled and one flat on each end.
I used red beveled ones on the (+) just so I'd have a polarity marker.
First I wrapped the battery with electrical tape to fatten it up.
The washers fit almost perfectly in shrink wrap - so they are easy to stack up.
Trim as you shrink - and the shrink wrap will draw the whole thing together.
The brass Bibb screws friction fit...I might add a pin drop of goop, just in case.
They seemed to work just fine in my TEAC ME-120s.
The parts (except shrink wrap) can all be re-used.
I am a bit concerned about the batteries mAh rating of 55...that seems low.
But - considering I use these mics somewhat infrequently...I dont think thats a problem...
The spec sheet says 81 hours at 8.8 V continuous discharge...
I like the idea that these batteries are cheap and available everywhere - so not a big deal to replace with fresh ones if its a important gig.