Kirkland 675's from Costco, I get 40 batteries for 9.99, I wasn't sure how long they last but I have that figured out now, about 3 weeks, maybe 3 1/2 and that's wearing my hearing aid from about 8:30 to anywhere between 8pm and midnight. Depends on if my ear is bugging, if it I take it out early, I tell my kids "I'm about to be deaf, do you have anything to declare?"