I’ve been wearing M90-13T HAs since last September. The size 13 batteries will last me about 8 days if I do next to no streaming, and 5½ days if I do a lot of streaming. The MyPhonak app claims I wear them about 14 hours a day. Over the 126 days that I’ve been wearing these HAs, I’ve gone through 21 pairs of batteries. That works out nicely to 6 days/pair of batteries. [I love easy math ]
For me, a lot of streaming would be around 2–3 hours streaming TV from a Roger Select, and another 2–3 hours streaming music while I’m walking the dog or cleaning up at night. The smaller, size 312 batteries have about 60% of the capacity of the size 13s, so one would likely get 3½–5 days between changes with them.
I buy a bunch of batteries on line about once a year, and pay about $0.50 per pair. The cost differential for lots of streaming versus having a streaming fast is about $0.25/ week.
The reason I went with batteries is I worried I might find myself on travel at some time and not able to get to a charger reliably. With batteries, one has no worries, provided one carries a few spares around.