Trying to revive a Apple Watch Series 4 in 2025 - Don't waste your time!

We have an orphaned Apple Watch Series 4, 40mm in May of 2025 running 10.6.1

The watch is considered obsolete.

The original battery health reports says that service needed.

I purchased a replacement battery from Amazon for under $20.  It included tools, but not the Y Wing screw driver needed to remove the battery. (The Y-Wing driver is a must along with tweezers).

I used a hair driver to soften the glue and using a suction cup to pry the screen off gently. (Make sure to fold it the correct orientation or you will rip the ribbon cables off.

There is no way to use an X-Acto knife without scratching a Space Grey phone. Accept that.

I followed the iFixit guide.

After putting everything back together, I realized the replacement battery was DOA.  It did not boot.

It made me think I broke the watch. 

The adhesive provided to reseal the watch sucks so I was able to put the old battery back in and it booted as normally and confirmed the supplied battery from Amazon was defective.

I was really annoyed as I could have kept the watch intact and it would be in a better condition then before attempting this fix. I did the Amazon Return.

Fast forward a couple days for me to cool off and I took a chance and bought another brand battery for the Series 4 and some E8000 glue. (Recommended on Reddit)

I was able to install the new battery and reseal it with the glue.

Phone booted and I was thrilled. (or so I thought).

I get only 4.5 hours from 100% to needing to be recharged. It was worse than the old battery I think.

I have an iPhone 15 Pro paired with it.

I tried turning off wifi and background app refresh, minimizing screen brightness and still can't get more than 4 and half hours or so.

After a couple days testing different setting options, it is pretty hopeless.

https://www.apple.com/batteries/maximizing-performance/

I give up.  10.6.1 probably doesn't play nice with new iPhones running the latest iOS.

Unpaired the watch and powered it off.  Recycle it goes.

I should have applied the money towards getting a new Apple Watch SE2 that was on sale  for $169.  Live and learn.