Well it’s not just metal cases that drain the batteries. I had mine in a plastic contact lens case and discovered they were all dead today. The only good part is discovering why. The tab is stuck to the back of the case which wraps around being exposed and the other terminal the nub is fully exposed. Put two of these together and they will bleed down. I don’t think covering the air holes is preventing them from being active.
Now I’m back to carrying them in the awkward circular plastic gizmo.