Even if they do work when new capacity will go down.
Like phones, vapes and all other li ions battery.
Don’t like that.
When i was taken to hospital last year because covid I spent 2 weeks in ICU. I had pack of 6 battery with me. So no hassle. Pair of battery is 6 day of hearing. And even if i didn’t, I could send family to supermarket to buy a pack and send me. It would be problem with external chargers.
Also I believe talking on phone drain a little more than streaming because aids have to transmit voice to phone. Imagine a late night romantic evening in restaurant after day of work and i have to wait 30 min to be able to hear in middle of dinning… 
Don’t want to think about battery every day…