I don’t have a PLB but… I wondered about the battery life. In general for something like this one should not push battery life to it’s max; so the question is “how replaceable is the battery”?
Quick google I see a product “ACR PLB_400”; spec sheet says “Battery Replacement 5 years” – this is good because it means that the battery can be replaced; and that the battery is “Non-hazmat Lithium Batteries (LiMnO2)”.
This is a “Lithium – Manganese Dioxide Battery (Li-MnO2) Batteries” – not a usual battery, I think, but it looks like every manufacturer makes them so they shouldn’t be hard to find.
So my assessment would be – test PRN and replace earlier than they say.
I think Nick is overdue for replacing his battery. 23 years is too optimistic for my taste.