[Retric]

> Generally, they're good for about eight hours.

That’s a function of how aircraft dropped sonobuoys are used. Subs aren’t going to stay still and the ocean is a big place so long lifespans are pointless. However for harbors you want continuous monitoring and so use a different design.

As to talking with satellites, that’s become very efficient at low bandwidth. If your 100W radio is off 98% of the time it doesn’t add up to a lot of energy.