Hearing aid batteries are expensive. No joke.
For standard behind the ear hearing aids and my particular model of cochlear implant, I've always had to use the largest hearing aid battery available: 675. When I used a hearing aid, I used one battery at a time and each one lasted roughly a week. In this cochlear implant, it takes three hearing aid batteries at a time (it's heavy on my ear some days) and they last roughly 3-5 days at a time.
In Target or the drugstore, you get a pack of eight 675 batteries at once. Each package costs between $8-10 depending on sales and sales taxes. I was lucky for a few years and Grandma would go crazy buying me hearing aid batteries when they were on sale with her seniors' discount. But that was before the Alzheimer's set in.
Luckily, a few years ago, I discovered Costco sells hearing aid batteries. They sell the hearing aid batteries in packs of 40...for $9.39 a pack. 40 hearing aid batteries for the same price as 8 batteries elsewhere. And these batteries last....usually about a week (so, longer than the packages I found elsewhere).
Suddenly, that $55 annual membership to Costco is absolutely worth it. I share this little find because I'm sure others out there are looking for the best prices on hearing aid batteries....or may someday find themselves needing hearing aid batteries too.