Some hearing aid models can use either rechargeable and non rechargeables. Seimens Pure 7px for one, and likely others.
I just did a VERY crude compare with the first prices I saw using Google. (I know, they’re probably cheaper somewhere, but these numbers I think tell the story.) enough.
Non rechargables size 312, 60 batteries for $21, assuming a 5 day life, used in pairs, calculates to $.14 per day, $51.10 per year.
Rechargable size 312, 2 batteries for $25.30, assuming they’re good for 1 year, calculates to $.07 per day, or $25.55 per year.
The rechargables might save a bit over a year, but you also must charge them once a day, and you add the potential failure of the charger and associated stuff on the H aids.
The non rechargables might cost a bit more but you get 5 or so days of continuous use without a nightly ritual.
The significant difference is only in how you view the differences.
And yes, the search for the perfect battery goes on. No different that anything else, if they could just pack more power into a smaller space…