Insight into the inside of the hearing aid

@gtremblay Thanks for the info on the batteries. I suspect they are actually building the batteries while you are waiting. I noted that some of the other alibaba offerings had wires welded to the case, but the ones you bought looked like they had no wires. Are you planning to spot weld wires to them or what?

Spot welding such a tiny copper wire to stainless steel is almost impossible. Moreover I want the new battery easily replacable the next time…

For now, I am planning to use this https://www.aliexpress.com/item/33040974988.html54
I will cut a circle slightly larger than the plastic casing and sitck the wires to the battery. This could also restore the waterproofing of the initial casing. Eventually it should be easy to remove and swap a new battery.

Unless I change my mind when I receive the new batteries.

@gtremblay said:

sitck the wires to the battery.

Using conductive glue or just a piece of tape?
I think this might be critical…

Look at the link above. It is not “just a piece of tape”. I will make a test with this material and see what happen. If not OK, I will use conductive glue.

I did think about it a bit more and if there is an ADC on the processor for battery level anyway then you would only really need to limit current.

You are right. The pads I have (from another project) are 1mm thick. They are not very sticky. But if I put a pad on each side of the battery, the total dimension (battery+2 pads) is about 1 mm larger than the corresponding dimension of the outside enveloppe. The wires are between the battery and the pads. Then I lightly compress this assembly and insert it in the enveloppe. Since the pads material is like stiff “memory foam”, it springback and wedge firmly the battery inside the enveloppe.

I did a test yesterday to confirm that. Hence, the next battery swapping will be a lot easyer.

I am happy that the batteries I ordered were shipped yesterday. I expect a delivery end of november…

By the way, I checket the voltage of the “dead” battery. It is almost zero (.5 mV). I will try to revive it by connecting it directly to a 5V source for a while. Who knows…

@gtremblay said:

By the way, I checket the voltage of the “dead” battery. It is almost zero (.5 mV). I will try to revive it by connecting it directly to a 5V source for a while. Who knows…

For slightly larger cells I use a disassembled 510 e-cigarette charger as the charger, the problem is they provide 420mA charge current which is almost a 20C charging rate for these which is definitely not good so maybe a 470Ω resistor as a current limiter?

To bump start I wouldn’t apply 5V for very long, as these are very small. 3.0V would be much easier going on the cell and would get it over any low voltage protection in the charger.

@gtremblay said:

Or remove it from the battery and connect it as the old battery?

Yes, I was just going to snip it off and solder the tabs to the existing enameled wire

@gtremblay said:

Oh! If the HA failed, could it be a BMS failure instead of a battery failure?

The voltage that you’ve quoted is practically 0V. It’s rare for cells to be so dead that the battery chemistry won’t test at least 1.0V under no load.
I think that cell failure is the most likely culprit but I don’t have enough experience to say how likely it is that an internal short in the BMS caused it.
I’ve had a Jabra Bluetooth earpiece go through a whole washing machine cycle in a soft water area that caused no damage at all, these sorts of things are very fickle!

The battery revival didn’t work.

If a lithium battery measures 0v there’s no going back. It’s generally due to hearing aid left uncharged for too long.

Interesting info. But I believe the distance between electrodes is larger than the HA battery.

I am expecting delivery of my batteries for Nov. 28. I am anxious to complete the job…

@gtremblay said:

But I believe the distance between electrodes is larger than the HA battery.

I think the probes could be bent to be closer together.
But will it work with a copper wire instead of the metall sheet?
Btw. I did a quick google search and found many cheap spot welding machines for batteries. Maybe an option.

Any high current source will do. I was just going to use a high amp power supply that I have but a 12v car battery will do, two batteries in series would be better but there are plenty of people on YouTube using a single car battery.

I was planning on cutting two small squares of nickel plate and soldering to those before spot welding to the battery. I do have some conductive tape too which might work too as discussed before.

I’m not having much luck sourcing a guinea pig device to practice on.

In some of “spot-welder” video (Youtube), there are probes which have sharp end and soldering is done by hand. Small nickel plate are used to solder the Li-battery together. Maybe a drop of silicon glue to be put on the soldering spot to protect the battery.