The item being replaced is a battery. The watches also have a capacitor in parallel with the battery which can drive the watch for some time while the battery is replaced. I suspect the capacitor also helps avoid pulling high (tiny high) current pulses from the battery as the hands are driven.

I can’t think of any reason to change from our two original 32 GB SE’s. Bought new two years for $130 and they do everything we need.

The most important thing, for us, is that they allow us to make phone calls and text messages. Any pictures we take are fine for the purpose and if we want superb photos we use a camera.

Yes, we did think about upgrading but the thrill went away, especially when we found out the it was glass on both sides.