Not a hardware engineer, but I'm going to wager that it has something to do with failure rates.
Modulo correct wiring, if you have a massive stack of D-cells and one dies, it's not a big deal. If your sole source of power dies, then you either have to send out a repair crew (expensive!) or have no data until the buoy is replaced on-schedule.
Modulo correct wiring, if you have a massive stack of D-cells and one dies, it's not a big deal. If your sole source of power dies, then you either have to send out a repair crew (expensive!) or have no data until the buoy is replaced on-schedule.