Need some help with an oddball battery and multimeter.
 

The Millett Zoom Dot scope on my M4 uses a 2L76 CR1/3N lithium battery. It stopped working at the range a while ago, so I bought a batch of three more such batteries from an eBay power seller. None of these batteries work in my scope and the one I thought was dead does work now. Seller says they test all their batteries and it's unlikely one, much less all three of them, are DOA.

I broke out my old Radio Shack multimeter, set it to 15v and am getting plenty of juice on the batteries. Am I testing them correctly? Can they be totally dead, but still making the needle move on my multimeter? Really frustrated here, since these batteries don't grow on trees.

Are they the right volt/amp? Check the battery contacts on the scope. Corrosion possible? Sounds like batteries test good.

Yes, the old and new batteries all have a + sign on the bottoms. If the old battery works and the new ones came right out of a sealed package, I don't think corrision is the issue. This is so frustrating. I feel like I need to test batteries before I buy them.

You have verified that you have enough Electrostatic Potential (voltage). But we don't know if you have enough Power.

P=IV

As stated, figure out the power requirement of the device (usually Watts for this kind of thing but my high school physics teacher was known to go to the hardware store and ask for a 0.00325 Horespower lightbulb).

Although a "constant" voltage source, batteries usually start to fall off voltage-wise as they get old. I'd say if you're reading more than the specified battery voltage, they probably are new. Then your problem is wrong battery.

If you're reading just under the specified battery voltage, then you've likely got bad/old batteries.