675 battery vs 13

i’ve pretty much decided my next pair of aids will be phonak.
been wearing aids for almost 40 years and until this last pair have always had the larger BTE using the 675 battery. my current pair are unitron BTEs using the 13 batteries. have had them about 4 years. I’m used to the 13 battery now but I remember when I first got them not liking the shorter battery life, like 10 days instead 3 weeks.

so now all 3 of the audis I’ve shopped with are pushing the 13 again. my question is why? I don’t mind the larger 675, in fact being larger the batteries are easier to handle. And I would definitely prefer changing batts less frequently. Plus there’s the difference in power/headroom between the SP aid and UP aid. Even though the SP should have enough power for me now it seems wise to have the extra headroom. my hearing has changed very little over the last 10 years but that’s not guarenteed for the next 10. Now that I’ve retired and living on fixed a income I want these aids to last more than 3 or 4 years.

but the audis don’t seem to think that should be a deciding factor(s) ???
what gives… what are they not telling me?
thanks,