The length of time that a hearing aid battery will last is dependant on three things and three things only:
1. How long you use your aids every day.
2. How much current your aids draw when in typical use.
3. The maH rating or capacity of the battery.
It is that simple really.
All batteries are not created equal as we have just discovered, but the differences in capacity for a given size, say a #312, are minimal it would seem. Hearing aid dealers would have you believe otherwise to sell you their preferred brand (the one that they make the most money on I surmise).
We were using their house brand for a while and then went out and bought 180 Power One #312's for $50 online. Almost a year's worth at the rate my wife uses them up. Going to order some Energizers, Panasonics, etc. to compare, but I suspect they are all going to be similar.
My recommendation in buying batteries is to buy from a reputable source. Storage or transport in extreme heat will cause the seal to break on the zinc air batteries and they will begin to discharge, so an expiry date of 2025 vs. 2015 makes little difference in that situation. You have no way of knowing how the batteries have been treated and often buying them online cheaply means that you have found a vendor who just bought a container load of batteries that were exposed to extreme heat or cold for an excessive period of time. Buying from a reputable source avoids this problem... a few bucks more, but guaranteed. AND THAT is the key. Energizers, if I am not mistaken, are "satisfaction or money back" and "if our batteries damage your equipment we will repair or replace your equipment". Need to check and see if that warranty still applies with all of their newfound competition these days.
Power One batteries have marginally more capacity than most others but not really enough to be noticeable under normal circumstances. We are playing with some now and they do seem to be lasting longer than the Energizers we were using but the Energizers may have been "surplus" from a hot container, etc.
For what it's worth.
250 Hz. - L=100; R=20 db.
500 Hz. - L=100; R=20 db.
1000Hz. - L=100; R=30 db.
2000Hz. - L=100; R=40 db.
4000Hz. - L=100; R=30 db.
8000Hz. - L=100; R=35 db.
Phonak Audeo S Smart V with BiCross and all the bells and whistles including Bluetooth, etc.
Herein lies opinion, not professional advice, which all are well advised to seek.