I confess that I have had hearing aids for more than 15 years (current age 68).
I just got a new set the other day and they provided (free of charge - HA!) a package of batteries. They had the company name on them and they are crap. They don't last long and there is no way I will buy from the folks who sell me the instruments. (For those who don't have them, the pros prefer to call them hearing instruments - go figure.)
For those of you who have them...where do you buy your batteries and why?