A quick comparison of the Series 5 with yesteryear's edition tells us ... very little actually. We'll need to put our spudgers to work mining for differences. To start with, here are the details we know:

LTPO OLED Retina display with Force Touch, optimized for always-on functionality

Custom-designed Apple 64-bit dual-core S5 SiP (System in Package)

Heart rate sensor and ECG

Comes in GPS-only or with optional LTE and brings a compass and ground elevation

Water resistance to a depth of 50 meters

The model number doesn't lie: A2157 tells us it really is a new Apple Watch.

Although the usual heat-and-slice action opens up the display, this model was clam-shelled shut a bit tighter than we expected.

The Force Touch gasket connector sits in its corner behind the display cables, where it moved with the last iteration.

Disconnecting the power requires first extracting the glued-down battery, which we know how to do (although we reserve the right to make a grumpy face as we do it).

This year’s energy source is labeled A2181 and provides 1.129 Wh (296 mAh at 3.814 V).

That amounts to a very slight 1.44% improvement over last year's 1.113 Wh battery. It's clear that battery improvements didn't drive the switch to the 18-hour always-on display—that technology is being enabled by something else.

Teardown Update: We cut into the smaller 40 mm Apple Watch Series 5, and found a surprising new battery design with a 10% capacity boost. We can only speculate as to why the 44 mm watch didn't get this upgrade, but you can read all about our findings over here.

The new LTPO display on the Series 5 (left) doesn’t seem to physically look all that different from last year's Series 4 display (right)—which also used LTPO technology. But Apple has been busily tinkering under the hood.

The LTE antenna connector occupies its usual spot, but a change in form factor prevents these displays from ever working interchangeably.

The resolution and dimensions are still the same: 368 × 448 pixels on the 44 mm version covering 977 sq mm.

After carefully tweezing the Taptic Engine away from an antenna connector, we can have a closer look for comparison.

Again, they look superficially very similar—but at the very least the connectors have been re-engineered, so we know the parts won't be compatible with last year's models.

With enough screws removed, the rest of the watch drops out the bottom, more or less as we remember from the Series 4:

We leave the digital crown, microphone, and side button clinging to the frame ...

... whereas the heart rate sensor, ECG components, and charging coil escape with the bottom plate.

We'll focus the rest of our attention on what's between: the S5.

Out comes this ticker’s brain, the all-new—or maybe not?—S5 system-in-package.

Although it benefits from a new compass and double the onboard storage—32 GB, up from 16—most of the integrated circuits remain entombed under a solid layer of resin, out of our reach. Of the few chips above the surface, here's what we can make out:

Skyworks 229-15 465371 1918 MX, most likely front-end module

16 CJ

YY NCJ 7NE (likely the acceleration + gyro sensor)

API 924 920

Looking at the attached display flex cables and laying them over those of the Series 4 for comparison, we can see that the plug in the middle gained 4 pins and the one on the bottom gained 2. Without knowing their function, this closes the door on interchangeability.

That's as far as we go. Although this year's always-on display is a huge leap forward in functionality, it's masked by surprisingly subtle changes in the underlying physical components.

Same basic construction, similar-looking components, and same amazing engineering in a mildly-annoying-to-open package. Plus a wild new battery design that only benefits the smaller version of the watch, for now.

What does it all mean in terms of repairability?

The Apple Watch Series 5 earns a 6 out of 10 on our repairability scale (10 is the easiest to repair):

Screen replacements are difficult but do-able—it's the first thing to come off, and detaches via ZIF connectors.

Battery replacements are pretty straightforward, once you're inside.

Still a lot of incredibly tiny tri-point screws are used throughout the watch.

Several component flex cables are mounted directly to the S5 package, requiring skilled microsoldering to replace.