There are many components involved in determining how long your hearing aid batteries will last. The size of the battery is one consideration. A smaller battery will naturally not last as long. Another consideration is how much power the hearing aid is using. If you have a lot of hearing loss or you are often in complex listening environments, your batteries will not last as long. One thing I recommend is to find out how long batteries last for your specific lifestyle. When you change your batteries put the battery sticker on that date on your calendar. This way, over time, you will get an idea of the average amount of days your batteries last.
Here are some very general guidelines for hearing aid battery life:
Size 10: 3-5 days
Size 312: 8-14 days
Size 13: 7-13 days
Size 675: 7-14 days