Replacing Logitech G930 cell with an 18650

[ziplock9000]

I have the old Logitech G930 wireless headset, who's battery is poorly performing now after several years.

Replacement batteries are 3.7V Lithium-ion usually between 600-800mah. However I'd like to replace it somehow with an 18650 cell as they are cheaper and I have tons

Ignoring the mechanical challenges fitting it, how would that work with a 18650's voltage going as high as 4.2v and would it charge correctly?

Also the normal replacement battery has 3 wires, black, yellow, red. Not sure if the 3rd is for cell balancing or not, or a temp sensor.

How would I get around that, thanks!

EDIT: According to some YT channel, the correct replacement battery has an internal protection circuit, so that would have to be added

[BeBuLamar]

3.7V and 4.2V are actually the same. The li-ion voltage will be about 4.2V when fully charge but they don't stay that way long at all. Then they spend most of their time between 4 to 3.7V. Below 3.7V they are considered dead
That aside a device designed to work with 3.7V most likely will work just fine at 4.2V.

[tunk]

It looks like it's a single cell, so it shouldn't need balancing.
As you mention, it could be temperature sensor.
Most 18650s has a max voltage of 4.2V, many flat li-po cells
have a higher 4.3-4.35V which may be a problem.

[BillyO]

Below 3.7V they are considered dead

For lithium-ion 3.5V - 3.7V is the nominal operating range.  They are considered dead at below 2.75V.  That is where most BMS systems cut them off.

https://cdn.shopify.com/s/files/1/0970/9262/files/typical_li_ion_discharge_voltage_curve.png?v=170427691

[BILLPOD]

Good Morning Ziplock9000,   I see replacement batteries are readily available, here's one at Amazon for 15 bucks:   https://www.amazon.com/Replacement-LOGITECH-Revolution-533-000018-F12440097/dp/B07PKK32WV/ref=sr_1_1_sspa?adgrpid=1346902316642063&dib=eyJ2IjoiMSJ9.px2LbOydObVmvalXiFHja4b9Gu4jVu9cBKFzR98Isgy0aDyTD9OlLwrSbpjVsLBZKJnKGKY_uVJV2-Ku-eDuVjYrrARoh76ywZZGnvjbJb9irdul6SnvMndNOKoFJI5EF2m2o0k0hcc0RwKthdhkOaIsWSAtuqLluDH68PQB63Jx0xBYF2ap43XUUqsOVvhCJZijvcQWMR5lwedPjq_Y0llfgDCyhKWNw02T6391I4s.hgYBMDaYiXKFXAevKEJve5Rv0dsY33dJGAR0mu683LE&dib_tag=se&hvadid=84181609212186&hvbmt=be&hvdev=c&hvlocphy=59456&hvnetw=o&hvqmt=e&hvtargid=kwd-84181757272305%3Aloc-190&hydadcr=19165_13351644&keywords=logitech+g930+battery+replacement&mcid=f52e0684c2103153b0ef00f00d4bdd6b&msclkid=f6ac452b2e6615556d4c2d2966d0c29f&qid=1744980184&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1  Looking at the form factor, I'm having a hard time picturing how an 18650 cell will fit into the headset.   Personally, I would fit a proper batt. in, and use my time
on other projects.

[ziplock9000]

Yeah I know there's replacement batteries, but as I mentioned in my OP I want to use the far cheaper and ubiquitous 18650s that I can just replace when needed. I also said don't worry about the physical implications. I don't intend to have it installed internally. Thanks though.

[BeBuLamar]

Yeah I know there's replacement batteries, but as I mentioned in my OP I want to use the far cheaper and ubiquitous 18650s that I can just replace when needed. I also said don't worry about the physical implications. I don't intend to have it installed internally. Thanks though.

If you can connect the battery and you can charge the battery (the original charging circuit may not be able to charge the larger battery well) then it's fine. The different in voltage (if actually any which I think none) would not be a problem.

[ziplock9000]

Yeah I know there's replacement batteries, but as I mentioned in my OP I want to use the far cheaper and ubiquitous 18650s that I can just replace when needed. I also said don't worry about the physical implications. I don't intend to have it installed internally. Thanks though.

If you can connect the battery and you can charge the battery (the original charging circuit may not be able to charge the larger battery well) then it's fine. The different in voltage (if actually any which I think none) would not be a problem.

I've seen other people mod this headset and they have used a resistor because the replacement battery's internal resistance is different to the standard one. They also use a protection circuit as the headset does not come with one and relies on the one inside the battery. The 18650's I have don't have protection built in. So this is why I'm hesitant to just hook it directly up like that.

[BeBuLamar]

The 18650 can put out at the most 4.2V no more than that. During the discharge cycle the voltage is more like 4V. I doubt that a device designed to work at 3.7V would be damaged if powered with 4.2V.

[tooki]

Below 3.7V they are considered dead

For lithium-ion 3.5V - 3.7V is the nominal operating range.  They are considered dead at below 2.75V.  That is where most BMS systems cut them off.

The BMS should be programmed to whatever cutoff voltage recommended by the particular cell datasheet. It can vary significantly. Most are close to 3V, but some are lower.

[BillyO]

Most are close to 3V, but some are lower.

I'm not convinced.  I can find very few (n0) Li-ion cells whose datasheets specifically put the lower limit at 3V.  That sounds more like Li-polymer.  All the Li-ion cells I currently have from Samsung, Panasonic and various Chinese manufacturers have the lower limit of 2.75V or less, some printed right on the battery.  Maybe I got lucky.  (The Samsung INR18650-32E I have specifies 2.5V)

The closest I can recall (well, in my notes) were some very old cells by Panasonic from an old IBM ThinkPad (770) battery I was trying to re-build.  The cells were CGR18650HM.  I just looked up the data sheet and it gives no specific lower voltage.  Most of the graphs stop a 3V, but not all.  The pathetic 1630mAh capacity for them was calculated from 4.2V to 3V.  So    However, they were from ancient times.  According to the notebook I was doing the re-build in 2005, so the batteries were probably pre-2000.  Technology may have come along a bit since then.

Here is a picture of an uninstalled Ultracell cell:
 

[amyk]

many flat li-po cells
have a higher 4.3-4.35V which may be a problem.

Only if you charge them that high - they will be fine when charged at 4.2V, just with less capacity. "High voltage" cells that go over 4.2V are designed with additives that make them last the usual rated number of cycles when charged to the higher voltage, giving a higher capacity, but they will last even longer when charged to 4.2V.

[tooki]

Most are close to 3V, but some are lower.

I'm not convinced.  I can find very few (n0) Li-ion cells whose datasheets specifically put the lower limit at 3V.  That sounds more like Li-polymer.  All the Li-ion cells I currently have from Samsung, Panasonic and various Chinese manufacturers have the lower limit of 2.75V or less, some printed right on the battery.  Maybe I got lucky.  (The Samsung INR18650-32E I have specifies 2.5V)

Look at the overview on page 14 of https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/INR18650_2D00_30Q_5F00_datasheet.PDF

2.75V is close to 3V, like I said. Some are lower, like 2.5V. My point, though, was that one should use the voltage specified for the cell in use, and not some guesstimated value.

[BadeBhaiya]

Skiming the thread, i think you should be able replace the cell with a normal 18650. The circuit should have charging+protection, everything to make it work. The probability that they use a different cell chemistry in this day and age is slim to none. If the circuit doesn't, it's trivial to buy a TP4056 based battery charging and protection board.

I think you should put some thought on the ergonomics of the entire headset. I have seen headphones fall into disuse after an "upgrade" just because the weight distribution or fit was changed because of the said upgrade.

[BillyO]

2.75V is close to 3V, like I said. Some are lower, like 2.5V. My point, though, was that one should use the voltage specified for the cell in use, and not some guesstimated value.

Under "Specifications", page 2, section 3.8 "Discharge cut-off voltage/End of discharge" - 2.5V as I said.

I'm not disputing that you should use the voltage specified.  My point was, and still is, that most readily available BMS cut off a 2.75 - that's it.  If you use such a BMS with the Samsung cell it will not damage it.  You may not tap into about 5% of the cell's capacity, but it will be fine.  If you really want to make things hard for yourself, sure, you could swap out the programming resistor.  Personally I would not bother.

[tooki]

2.75V is close to 3V, like I said. Some are lower, like 2.5V. My point, though, was that one should use the voltage specified for the cell in use, and not some guesstimated value.

Under "Specifications", page 2, section 3.8 "Discharge cut-off voltage/End of discharge" - 2.5V as I said.

Yes, for that specific cell, which is one for power tools. But most are higher, as shown in the table I linked. But again, my point is that one should use the voltage specified by the cell, and not a voltage suggestion by someone on a forum…