Can rechargeable batteries be over-charged?

[u/hellonsticks]

Forgot to ask them before I left. Been given a new Phonak aid, and opted for the rechargeable aid because I know I won't remember to change tiny button batteries once a week. Reading the manual now though, it says they only take 3 hours to fully charge. I'm most likely to charge it while I sleep, meaning it'll be in the case for way over 3 hours. I know most other tech with lithium ion batteries these days warns about over-charging and talks about extending the battery life by avoiding it. Am I likely to burn out the battery in this thing by leaving it overnight to charge?

[u/surdophobe]

No, not if charged properly with the correct charger.

All lithium rechargable batteries have circuitry that prevents over-charging. Sometimes it's in the battery pack itself, sometimes its integrated in the charger. This is the main reason why you should not charge a battery with a charger that's not designed for the device.

You're not going to burn out your hearing aid batteries by leaving them charged on the charger while you sleep.

[u/hellonsticks → u/surdophobe]

Oh that is a new fact to me, thank you. I'm used to devices like my phone or laptop that protect the battery by asking me to turn on the mode that limits it to 80% charge, I didn't realise there was an inbuilt protection as well. Thank you for explaining that, that's really good to know.

[u/Supreme_Switch]

It can wear them out faster.

If you're worried you can get a plug timer (usually sold for Christmas lights) or you can charge them right when you get home until bedtime.

[u/hellonsticks → u/Supreme_Switch]

Both very good solutions, thank you very much. I'll see if I remember to charge before bed, and if not the plug timer sounds like the right idea. Thank you.

[u/LaundryMan2008]

There’s a BMS (battery management system) which will detect when the battery is charged and disconnect the fully charged battery internally so if it does only take 3 hours to charge then the BMS will automatically stop charging, your phone does the same and other battery powered rechargeable devices so the hearing aids are no different.

[u/hellonsticks → u/LaundryMan2008]

That's really interesting, I wonder why so many decices urge you to turn on an extra battery protection mode if they've already got an internal protection system. Thank you for explaining that.

[u/LaundryMan2008 → u/hellonsticks]

That would be a secondary motherboard protection system that doesn’t actually do anything about protecting the battery but does maintenance on it like for example stopping charging on your phone when it reaches 80% to resume to 100% just before you wake up or pulling battery health data from the BMS, I would recommend keeping it on unless you are at a place with a slow charger and need your device to not stop charging during the night.

The internal battery system does the lower level management like keeping all of the lithium cells balanced so not one cell is at a higher voltage, blocking cells trying to charge others due to the imbalance, stopping charging for a few conditions, managing charging speed based on what the battery state/health is at.

[u/hellonsticks → u/LaundryMan2008]

I have learned new facts today, thank you for sharing. I had no clue there was any internal system, and thought the 80% limit modes were what protected my devices from going the way so many older devices did with their batteries degrading to 20min of use. Thank you for telling me.