Doug -- Is battery type an FCC issue or an FAA issue? Seems FCC shouldn't care, but FAA very much cares that the unit have stringent battery life/reliability specs.

With a rechargeable battery that spec would be lost. Even with zero leakage, when was it last used and when was it last recharged?

Perhaps a non-FAA compliant PLB could be made for non-aircraft use that uses a rechargeable battery, but would it be in the manufacturer's interest to make it? Who gets blamed when the rechargeable isn't and the battery fails?

Thinking out loud . .