If I was fitting new batteries to your ELT, then you're quite correct, "standard" AA's would be bogus parts.
HOWEVER! My post was a cut and paste direct from the manufacturers overhaul documents, where "six standard 1½ volt “AA” size batteries" is the specification. So, as long as the batteries are of AA size, produce 1.5 volts, and you fit 6 of them, it's all good!
That is indeed the megaphone in question, and it IS actually certified, just not for $350!
This is something we see quite often, the last example was buying some multi-meters off the shelf at the local tool store (multi-meters listed in the approved maintenance data obviously). £120 to Joe Public, £240 for the exact same thing with a certificate in the box.
lomapaseo, quite correct, I knew some were Ti and some were cad plated, I've gotten the 2 mixed up!