Hi. I've been having the same
Hi. I've been having the same problem with my 2015 used outback I bought from Ohio. I'm currently living in MI and my battery has died multiple time. I've done extensive research and I finally found a guy who can answer your question about beefing up your battery to fix the problem. I have yet to change my battery and going to do so ASAP. Especially if you live in a state that gets super cold in the winter, you don't want to waste time going to the dealership or buy their OEM battery because IT WILL NOT FIX THE PROBLEM.
If anyone has questions about buying a bigger better or better yet a battery with a higher cold start or CCA, go and watch Charles Cupp youtube channel and search for "2016 Subaru Outback group 24 Battery".
Hope this helps and good luck!