I don't understand why the pingers are on continuously until battery depletion. Assuming we can't have them be triggered by incoming sound (making them essentially sonar transponders), why couldn't they be on for e.g. 15 days, then off for a month, on for 7 days, off for two more months and on for 7 days? The power requirements of the timing device are minuscule (my watch needs a new battery every few years).
How would turning the pinger off for a month help? It just means that the search operation stops for a whole month while they wait for the pings to resume. I don't understand how your proposed idea would benefit a rescue operation.
I'd suggest something more sensible. E.g. one ping every Ns for the first 15 days, every 2Ns for the next 15 days, every 4Ns for the next 15 days... oh look, "infinite" duration.
However, I suspect the "pinger" mechanism is very, very simple and completely analog. No logic in its circuit at all. Because having it SURVIVE to ping 30d was the key consideration.
