Hmm really? My Camry made it nearly 10 years, and my Civic still had a good battery 6 years in when I sold it.
Regardless, the battery and DCM were both tested by Subaru. The battery tested bad, and the DCM tested for a high parasitic draw. I drove the car daily, and the battery would die if I didn't drive it for 4 days. I didn't just make this up either, search "DCM parasitic draw" on Google for more. Subaru even sent me a letter outlining my options for repairs.
Lots of places will say an average car battery's life is somewhere around 3-5 years. It is highly dependent on weather. Here where there are regularly long spans of 100F+ days, a battery will have done pretty good to make it five years; many die in 3-4. Same in very cold climates. If you're in a place with good weather all the time they'll last considerably longer.
I've heard about this being a known issue with cars from other manufacturers, so I can believe it. It's interesting that nobody thought to include a way to let the vehicle know it should stop trying to communicate to handle a potential end-of-service situation like this. It's fairly common for people to keep cars for more than a decade, they're a really expensive necessity for many.
That's a known issue. Reports all over the subaru forums.
I tried to measure it myself with my little multimeter and now I don't have a working multimeter.
One suggestion I tried that seemed to work was to not keep the key close to the car, since that'd not physically possible for me I wrap it in an ESD bag. Haven't had much issue since, but no promises.
Regardless, the battery and DCM were both tested by Subaru. The battery tested bad, and the DCM tested for a high parasitic draw. I drove the car daily, and the battery would die if I didn't drive it for 4 days. I didn't just make this up either, search "DCM parasitic draw" on Google for more. Subaru even sent me a letter outlining my options for repairs.