It would be interesting to know though, how much battery replacement is.

I will ask next week during my follow up session with my audiologist and report back.

In general, for lithium-ion or lithium polymer batteries, staying between 20% and 80% and restricting the depth of discharge gives the longest battery lifespan in terms of full-equivalent charge cycles (charging 20% 5x counts as one full-equivalent recharge cycle). I think Phonak has stated, though, that the batteries are expected to last five years (you might not get the same runtime five years down the road that you get brand-new). Presumably, in making that statement, they’re allowing for all the folks who just plain charge away to 100% every night and use the batteries down to the level that you get an HA recharge warning. So one approach would be, “What me worry?!” (Mad magazine, Alfred E. Neumann, for you youngsters).

I think with manufacturers, you have to allow for the fact that in their charging advice, there’s PR mixed in with charging physics. They want you to be happy with your instruments and not feel hassled about charging them according to any rigorous routine. But I have a two-year-old iPhone 14 Pro Max and an Apple Watch Ultra, both kept between 40% and 60% SOC almost the whole time since I’m an old, at-home retiree. The battery health of both is still rated at 100% two years in. So, if you really want your device to last forever, try something like that if you have time and patience. It’s not practical for most people.

If you live in a hot climate, no matter how you charge your HAs, it’s probably not good to expose them to extreme heat. Heat is the enemy of Li-ion batteries, particularly when they’re very highly charged. Manuals for both rechargeable and disposable battery-powered ReSound HAs say not to use them above ~104F; the Phonak Lumity manual says the same, IIRC. Apple says not to use most of their devices above 95F.

Since folks on this forum are reporting run times for the Sphere i90 of as much as 31 hours without much streaming or Spheric noise reduction use, you could follow a routine of keeping the charge between 20% and 80% SOC (60% of capacity x 31 hours full capacity use ≈ 18 hours of use on 60% charge. Some devices prevent their batteries from being fully charged or discharged by blocking the user from entering the highest and lowest charge states when charging or discharging the devices. I don’t recall any evidence that Phonak does that with their devices. But providing batteries with excess usable capacity and restricting users to the middle ground would be one way to make batteries last longer. A bigger battery adds to the cost of the device and requires more space. But, hey, the Sphere is superior to the Lumity for that reason, too!

Unless the charger is designed for an early shut off, there’s no way to know unless I throw a dvm on it. It’s not programmable. Not sure if we can even find specs for it.

I’ll have to put my big fluke scope/dvm on it.

Those pins on the ha are really close

@jeffpa said:

High or low charge states don’t matter at all to cell chemistry.

The world seems to disagree a wee bit…

MS Copilot:

Does the time spent at high or low charge states affect the long-term life span of Li batteries found in personal devices like smartphones, smartwatches, and hearing aids?

Copilot

Yes, the time spent at high or low charge states can indeed affect the long-term lifespan of lithium-ion (Li-ion) batteries in personal devices like smartphones, smartwatches, and hearing aids1.

High charge states (close to 100% charge) and low charge states (close to 0% charge) can both stress the battery and lead to a shorter lifespan1. It’s generally recommended to keep the battery’s state of charge between 20% and 80% for optimal longevity1. This reduces stress on the battery and helps prolong its life1.

Additionally, rapid charging or discharging can generate more heat and put extra stress on the battery, potentially leading to a shorter lifespan2. Following the manufacturer’s recommended charging rates is advisable to ensure optimal battery health2.

1. BU-808: How to Prolong Lithium-based Batteries - Battery University1

2. Lithium Battery Lifespan: Expectations for Charging Cycles (tritekbattery.com)

Conversation with Gemini

Does the time spent at high or low charge states affect the long-term life span of Li batteries found in personal devices like smartphones, smartwatches, and hearing aids?

Yes, the time spent at high or low charge states can significantly affect the long-term lifespan of Li batteries in personal devices.

Here’s a breakdown of why:

• High Charge States:
  • Chemical degradation: Prolonged exposure to high charge states can accelerate chemical reactions within the battery, leading to the formation of unwanted compounds that reduce capacity and lifespan.
  • Heat generation: Higher charge states can generate more heat, which can further accelerate degradation and even lead to safety concerns.
• Low Charge States:
  • Parasitic discharge: Even when not in use, batteries experience a slow parasitic discharge. If left at a very low charge for extended periods, this discharge can eventually lead to complete depletion and damage.

To maximize battery lifespan:

• Avoid extremes: Try to keep your battery’s charge level between 20% and 80%.
• Regular charging: Don’t let your battery completely drain before charging it.
• Avoid heat: Keep your device away from excessive heat sources.

By following these guidelines, you can significantly extend the life of your device’s battery.

Sources and related content
Lithium-ion batteries in use: 5 more tips for a longer lifespan | Saft
4
Deep Dive: Lithium Ion Batteries and Heat - Recurrent

Best Practices for Charging Li-ion Batteries - FireBoard Labs

Good points, Profile - jim_lewis - Hearing Aid Forum - Active Hearing Loss Community

Extra credit for the Alfred E. Neumann reference!

All this technical stuff reminds me why I dropped out of engineering school and changed majors. But, I digress.

The key concept I was missing (that you highlight) is that a recharge from 60 percent back to full charge using my Phonak charger is not a “cycle” as that term is used in literature explaining that a Li-Ion battery is rated for only a certain number of cycles. Instead, it might be considered 40 percent of a “cycle”.

So, my non-technical brain concludes, don’t worry about using too many cycles by charging every night. It all comes out in the wash.

as Roseanne Roseannadanna might say, since I started us down this rabbit hole, “never mind”. I will charge every night.

@jeffpa said:

where is it documented you can get new batteries before the 3 years?

Manufacturer servicing will invariably include a battery change, or they will just replace the whole aid rather than attempted servicing by local techs. If they are breaking the shell open, there’s going to be a module changed, nobody’s going to mess with chopping welded bits out.

It might seem illogical, but the cost of running a capable service tech is far higher than swapping the whole aid - plus you lose the original manufacturing integrity once you open the case.

Interesting point on the internal electronics, which seem to indicate a BMS system (Battery Maintenance/Management) which makes a good design and why I couldnt get any voltage at all on the pins.

@jeffpa, do you have access to material/articles that convincingly explain why rechargeables are preferable to disposables in terms of advanced features of sound processors/HAs?

For example, Cochlear claims that rechargeable batteries provide more power compared to disposable (I think it’s about instantaneous power), even though they provide a shorter processor time (20 hours for the larger battery compared to 35 hours for the 2x zinc-air 675):

While I havent read what you provided, I can say that lithiums provide more consistent voltage for longer periods of time in a small footprint (capacity) at higher rates of discharge. The discharge curves, especially at what I’ll assume is an extremely low discharge rate are very flat other than an initial voltage drop from peak charge. And the initial drop is dependent upon internal resistance of the cell itself as well as the discharge ratre.

@1Bluejay - This is exactly what I do with my rechargeable Oticon CROS loaner. I just drop it in my charging base overnight.

@jeffpa said:

Interesting point on the internal electronics, which seem to indicate a BMS system (Battery Maintenance/Management) which makes a good design and why I couldnt get any voltage at all on the pins.

You mean pins on the HA or on the charger?

the charger is 5v at the pins, I’m taking about pins on the HA.

Thanks for your reply. I think now the HA pins mustn’t have any potential difference due to sweating on the ear.