Series 1 Repair - Minimum Battery Voltage?

[Jstluise]

Tl;dr What is the minimum battery voltage required for the Series 1 to boot/charge?

I'm hoping someone here might know this or can point me in the right direction before I give up. I'm attempting to repair a Series 1 after it went dead on me. The watch would only show signs of life on the charger, but even then it was in the Apple logo boot loop. All signs pointed to it being a bad battery, so I got a kit from iFixit.

I replaced the battery but still experienced the same issue. I measured the replacement battery voltage at 2.35V which seems low for a 3.8V nominal battery. The original battery was 1.8V.

I got another replacement battery, but again no luck and it measured 2.37V.

Seems unlikely that I would get two bad batteries in a row, but those voltages seem low to me. I can't find info on Apple watch battery voltages anywhere...does anyone know?

Thanks!

 

[mj_]

If my memory serves me right a standard 3.6V Lithium-Ion battery cell should not drop below 2.5 V, otherwise a regular charger might not be able to charge it ever again because its internal resistance would be too high for a charger to overcome it. Depending on manufacturer some cells can go as low as 2.2 V, others will stop working at 2.9 V but the average is 2.5 V. Given that the Apple Watch battery's is specified at 3.8 V I would assume these numbers to apply to that battery as well.

In other words: 2.35V seem very low for a 3.8V battery if you ask me. A few years ago I've had major issues with several high-quality 3.6V Panasonic 18650 batteries that dropped below 2.8 V and refused to take a charge. I had to trickle charge them for 48 hours before they were capable of accepting a charge again. Have you tried simply leaving your watch on the charger for 24 hours or more before attempting to turn it back on?

 

[mj_]

FYI, I've just ordered one from Amazon for my 42mm S0. I can you know what its voltage is and whether or not it's working next week when it has arrived.

 

[Jstluise]

If my memory serves me right a standard 3.6V Lithium-Ion battery cell should not drop below 2.5 V, otherwise a regular charger might not be able to charge it ever again because its internal resistance would be too high for a charger to overcome it. Depending on manufacturer some cells can go as low as 2.2 V, others will stop working at 2.9 V but the average is 2.5 V. Given that the Apple Watch battery's is specified at 3.8 V I would assume these numbers to apply to that battery as well.

In other words: 2.35V seem very low for a 3.8V battery if you ask me. A few years ago I've had major issues with several high-quality 3.6V Panasonic 18650 batteries that dropped below 2.8 V and refused to take a charge. I had to trickle charge them for 48 hours before they were capable of accepting a charge again. Have you tried simply leaving your watch on the charger for 24 hours or more before attempting to turn it back on?

Thanks for the reply. I agree with everything you said and this lines up with my experience with lipo packs for RC airplanes. Under load, the absolute minimum voltage you want to go is 3.0V and typically you stop around 3.3-3.4V to be safe. After the load is removed, even if the battery is fully depleted, the resting voltage should return to close to nominal of 3.7V. Fully charged is 4.2V.

I also found some info on iPhone batteries which said something similar: 3.0-3.1V is the minimum voltage that the phone will operate. I would assume the watch would be similar.

So yeah, I agree that 2.35V is real low and too low to take a charge. With the first replacement battery, through various button pushing and taking it on and off the charger, I was able to get the green charging snake screen to show up; however, even after leaving it on the charger for a couple hours I still couldn't get it to boot and the watch just got hot. No luck getting that screen again.

FYI, I've just ordered one from Amazon for my 42mm S0. I can you know what its voltage is and whether or not it's working next week when it has arrived.

Sure, that'd be great! One thing to note is that I wasn't able to get a voltage reading off the battery connector...I couldn't seem to figure out the pinout. Instead I peeled back the battery cover next to the connector to reveal the battery pads and used some sharp pins to take a reading since the pads have a coating on them

I am going to contact iFixit again for another replacement...

Thanks!

 

[mj_]

Quick update: I was unfortunately unable to read the voltage on the new battery as the terminals were covered with some sort of plastic even after peeling back the housing, as you suggested. It worked on the old battery, and I got a reading of 3.78V with the battery around half empty. With the new battery installed I did have to put the watch on the charger for around 30 minutes before it powered on. During these 30 minutes it did display the low battery but charging graphics where the lightning bolt in the upper left corner was green, and it turned on by itself once it had reach a sufficient charge level.

 

[Jstluise]

Quick update: I was unfortunately unable to read the voltage on the new battery as the terminals were covered with some sort of plastic even after peeling back the housing, as you suggested. It worked on the old battery, and I got a reading of 3.78V with the battery around half empty. With the new battery installed I did have to put the watch on the charger for around 30 minutes before it powered on. During these 30 minutes it did display the low battery but charging graphics where the lightning bolt in the upper left corner was green, and it turned on by itself once it had reach a sufficient charge level.

Great! Thanks for the info! That makes me very certain the batteries I have are defective. I'm working with iFixit to get another replacement...crossing my fingers the next one will be good otherwise I may source the battery from somewhere else.

 

[mj_]

You may have to, although it would surprise me given that iFixit is usually very reliable. Either way, this is the battery I bought: https://www.amazon.com/gp/product/B07V3ZX7QN

As of right now I can't really tell you how well it works because the Forch Touch sensor gasket disintegrated when I was prying off the screen, so I'm currently waiting for a new one that is supposed to arrive by Wednesday evening. Once I've reassembled the watch and have used it for a few days I will be able to let you know whether or not that battery is actually any good.

 

[Jstluise]

You may have to, although it would surprise me given that iFixit is usually very reliable. Either way, this is the battery I bought: https://www.amazon.com/gp/product/B07V3ZX7QN

As of right now I can't really tell you how well it works because the Forch Touch sensor gasket disintegrated when I was prying off the screen, so I'm currently waiting for a new one that is supposed to arrive by Wednesday evening. Once I've reassembled the watch and have used it for a few days I will be able to let you know whether or not that battery is actually any good.

iFixit sent me another battery and I measured the voltage before installing it: 2.23V. Again, too low. I installed it anyways and put it on the charger. The Apple icon popped up and then the green charging snake actually showed up (this happened with the 1st replacement battery, too). I left it alone for 2 hours and came back to no change as I suspected. I wasn't able to get the watch to boot or reset, and the screen goes off as soon as it is pulled from the charger. Same results as before.

So that's 3 batteries in a row, all with roughly the same low 2.2-2.4 voltages. This seems strange so I'm going to ask iFixit if other customers are reporting the same. I went with iFixit because I thought I would be getting a better/more reliable battery than something on Amazon/eBay, but I may have try something else.

 

[valynor]

That's definitely not OK.
LiIon/LiPoly cells can become physically damaged and unsafe to use when discharged below 2.5-2.8V (varies with the cell chemistry).
A new cell from the store should be somewhere around 3.6-3.9V.

Either your "new" batteries are straight up defective or they have been lying around for many months/years.

 

[Jstluise]

That's definitely not OK. LiIon/LiPoly cells can become physically damaged and unsafe to use when discharged below 2.5-2.8V (varies with the cell chemistry).
A new cell from the store should be somewhere around 3.6-3.9V.

Either your new batteries are straight up defective or they have been lying around for months/years.

Since these batteries only work for S0/S1, my guess is that they've just been sitting around for a very long time. I had to wait a little while to get my 1st replacement because iFixit was out of stock until around Aug-20, so something is up with their latest lot of replacements. I did see a few posts over on the iFixit forum reporting the same problem.

 

[mj_]

I agree, this is definitely not normal. It's possible that their last batch is simply bad, and I suspect it's because they've been stored improperly. The self-discharge rate on modern lithium-ion and lithium-polymer batteries is so low that if charged to 80 % and stored properly (read: in a cool, dry place) they can last over a decade before dying.

 

[Jstluise]

I received battery #4 from iFixit: 2.25V. No luck. At this point I may just try to get a complete refund from them and throw in the towel, maybe sell the watch for parts. Or maybe give Amazon a try one time. I was planning to sell the watch anyways once I got it running, so this has become much more of a timesuck than I was anticipating.

 

[Jstluise]

As one last attempt I ordered a couple batteries off Amazon. I measured both out of the box, one was 1.4V and one was 2.2V. Not was I was hoping for but I tried both anyway. I was able to get the green charging snake with each battery, but still had no luck after a couple hours of sitting on the charger...same results as the rest. The 1.4V battery did measure 2.3V after removing it and letting it rest, so it did take some charge.

I still think the issue is with the batteries...I haven't really been convinced otherwise. But after the same results with 6 batteries maybe the issue is with the watch. iFixit was nice enough to refund me, so I think I'll just throw in the towel and sell the watch for parts.