University 12.5mm Ortho Reticle Battery

Does anyone know what battery this uses?

I recently bought this used University 12.5mm Ortho Reticle Eyepiece.
The seller had removed the battery, and is not responding to emails.
University Optics has not replied to my emails either.
There are no markings anywhere on this reqarding voltage or size.
I've had the illuminator to Radio Shack and Battery Mart and they have no idea.

Any help would be appreciated
Fred Dase

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They are the little button batteries ( (2-SR44 camera batteries), I think two of them, but not certain. If you take it to a store you can see the sizes available and find the one that fits. Should have the solid cap to the bottom I believe and the button to the top. But it won't hurt if it is backward, it just won't light, so turn them around.
It looks just like my Parks reticle as far as the switch and battery holder is concerned and this and the Meade both take these batteries.

U.O. got back to ma concerning the battery.
Tom was right it used the 2.7v PX14 Mercury Battery.
I'll try the 3v PX14 replacement and see what happens.
Thanks everyone for the help.
Fred Dase