I’m personally a huge lithium battery and rechargeable fan. I’ve worked on lots of custom battery projects out of lithium cells from custom e-bikes, RC cars or portable battery packs. I’m working on a custom battery pack right now for our handheld ham radios that we use for racing and building the battery pack out of regular 18650 lithium batteries. It’s amazing what you can do with these batteries and for such a small cost.
The rechargeable batteries in these hearing aids are subject to the same battery principles for any lithium based cell. They are good for a certain number of charge cycles, and they lose X% of their overall capacity with each charge cycle depending on how deep the charge cycle went and other factors like heat, rate of charge, etc. I expect Phonak sourced high quality cells and tested them well to meet the manufacturers specs, so barring manufacturing defects, you are left with the regular lifespan of a lithium cell. They can vary a bit based on a lot of factors, but the general rule of thumb is that a lithium cell with lose about 15% of it’s maximum capacity after 250 charge cycles. A full charge cycle is running the battery dead, and modern electronics shut the devices off at the proper minimum voltage.So a charge cycle for someone who runs their hearing aids down to only 50% each night is theoretically is only using half a charge cycle and won’t lose as much capacity with each charge. Smaller cycles in the middle of the charging range makes a huge improvement in battery life and stress, but no one wants to pull their phone or hearing aids off the charger at 60% and run them to 40% several times per day. In the end, a hearing aid battery may still work after 5 or 6 years, but it will have likely have less than half the capacity at that point and may not really be usable.
Battery tech is really incredible and it’s advancing fast in some areas, but so slow in others. Battery University is a great resource on how batteries work and how you can prolong the life of your batteries. There are a lot of battery myths out there with battery memory, charging, etc. that persist out there that just don’t exist anymore.
My biggest gripe with the rechargeable hearing aids is when I go to bed. Sometimes I like to talk to my wife as we fall asleep. I’ll keep my right hearing aid in until she’s out or until it’s time to roll over and I’ll pull my HA and pop the door cover and lay it on the nightstand. Or… I’ll turn on the light, open the lid to the charger, drop it in, close the lid and go to sleep. Maybe I’ll learn how to do that in the dark, but it’s a pain. I’m totally spoiled from having worn the Lyrics for the last 10 years which allowed me to hear 24x7 and change the hearing aids every 3 months. You really take that stuff for granted with a switch like this. I really miss being able to hear 24x7.