Spring steel piece not to lose before removing motor shaft from housing!

Added this under step 7 but placing here too.

Critical: BEFORE removing the motor shaft from the second half of the outer casing in Step 8, carefully examine the inside part of the button you press to hold the shaft stationary (while you install/switch bits/tighten the chuck). There’s a C-shaped piece of spring steel on the inside of the unit, which has a little hole in it, that in turn sits on a little pin that is on the internal side of that shaft-holding button. It’s what causes that button to pop back out again after you’ve switched bits, freeing the shaft to spin again.

You must be able to carefully remove the motor shaft while observing how that spring steel sits in the inside of the button and not drop or lose it, otherwise the button will no longer pop back out and free the shaft after reassembly!

Kudos to the hero whose original comment I read that warned ME about this, a comment which I now can no longer find to credit.

Spring steel you must observe/keep/reinstall!

Critical note: BEFORE removing the motor shaft out of the second half of the outer casing in Step 8, carefully examine the inside part of the button you press to hold the shaft stationary (while you install/switch bits/tighten the chuck). There’s a C-shaped piece of spring steel on the inside of the unit, which has a little hole in it, that in turn sits on a little pin that is on the internal side of that shaft-holding button. It’s what causes that button to pop back out again after you’ve switched bits, freeing the shaft to spin again.

You must be able to carefully remove the motor shaft while observing how that spring steel sits in the inside of the button and not drop or lose it, because if you reassemble without it, the button will not spring back out and free the shaft after bit installation.

Kudos to the hero whose original comment I read that warned ME about this, a comment which I now can no longer find to credit the writer.

Replaced my Series 1 battery/force sensor. The swelled original battery popped the watch open, so no prying necessary. However, the watch wouldn't work normally afterward, only displaying the "put me on my charger!" image of the charge cord with the disc on the end.

iFixIt was great about sending a replacement... battery, tools, force touch sensor, the whole kit, no charge. Replacement #2 required prying it open, but the force touch sensor stayed put, so I didn't have to replace that the second time. Watch is charging and behaving normally as I calibrate the battery. Can unlock etc.

Be very gentle/careful with the tiny force touch sensor screw. A great comment above says if you lose it, you can put in bit of a pick to press the sensor snug where the screw would hold it. I strongly recommend using a cheap hands-free, head-mounted magnifier w/light for this job. A loop of tape to stick the watch to a surface to hold it still while fiddling with the tiny cable connections was a HUGE help. Take your time!

Replaced my Series 1 battery/force sensor. The swelled original battery popped the watch open, so no prying necessary. However, the watch wouldn't work normally afterward, only displaying the "put me on my charger!" image of the charge cord with the disc on the end.

iFixIt was great about sending a replacement... battery, tools, force touch sensor, the whole kit, no charge. Replacement #2 required prying it open, but the force touch sensor stayed put, so I didn't have to replace that the second time. Watch is charging and behaving normally as I calibrate the battery. Can unlock etc.

Be very gentle/careful with the tiny force touch sensor screw. A great comment above says if you lose it, you can put in bit of a pick to press the sensor snug where the screw would hold it. I strongly recommend using a cheap hands-free, head-mounted magnifier w/light for this job. A loop of tape to stick the watch to a surface to hold it still while fiddling with the tiny cable connections was a HUGE help. Take your time!

Replaced my Series 1 battery/force sensor. The swelled original battery popped the watch open, so no prying necessary. However, the watch wouldn't work normally afterward, only displaying the "put me on my charger!" image of the charge cord with the disc on the end.

iFixIt was great about sending a replacement... battery, tools, force touch sensor, the whole kit, no charge. Replacement #2 required prying it open, but the force touch sensor stayed put, so I didn't have to replace that the second time. Watch is charging and behaving normally as I calibrate the battery. Can unlock etc.

Be very gentle/careful with the tiny force touch sensor screw. A great comment above says if you lose it, you can put in bit of a pick to press the sensor snug where the screw would hold it. I strongly recommend using a cheap hands-free, head-mounted magnifier w/light for this job. A loop of tape to stick the watch to a surface to hold it still while fiddling with the tiny cable connections was a HUGE help. Take your time!

Thanks a ton for this. I'm hoping I won't need it, but knowing the parts only need to be in contact, not necessarily held together with the screw, is huge to know. My first battery replacement didn't result in a working watch, but the replacement kit iFixIt sent and second battery replacement seems ok. I replaced the force touch sensor the first time, as it peeled apart/was clearly ruined. After prying the watch face off for the second replacement, the force touch sensor stayed in place, which I'm very grateful for, because that darn tiny teeny screw just HAS to be stripped after I had to take it in and out a few times during the first replacement. Force touch seems to work, so I may not need to replace the sensor this time (fingers crossed), but knowing doing it without the screw if it's stripped is an option is enormously helpful.

I had a similar experience. After battery replacement, my watch would only show the sort of spaghetti image of the charge cable on its screen (i.e. "put me on my charger, please!"). It reacted when I did put it on the charger as if it was charging, but never actually did, nor did it seem to run flat and shut itself off. iFixIt sent a new battery kit at not charge, tools, force touch sensor, and all. After putting that battery in, the watch behaves normally so far. I put it on the charger, it powered up, said it was at 93% (may be miscalibrated... I'm calibrating it now), and charged up to 100%. While doing that, I could put in the unlock code, run apps, etc, not stuck on the "charge me" screen. So it wasn't completely dead after the first battery replacement, but never really came back to life either. After second replacement, it's behaving as it should.

The box my IFIXIT replacement battery came in has battery calibration steps printed on one side, to wit: "Charge your newly installed battery up to 100% and keep charging it for at least 2 more hours. Then use your device until it shuts off due to low battery. Finally, charge it uninterrupted to 100%."