What kind of battery lasts seven years but not 15 or 20 years?

They claim the GPS receiver has 66 channels, which is far more than needed for the GPS constellation, far more than can even be used.

Perhaps it can listen to the European and other constellations? But I wonder why? COSPAS/SARSAT already can't receive the full resolution of civilian GPS receivers - 406 beacons already have to discard a little position precision. Perhaps the other constellations allow for a faster cold-start fix?