Just to summarise, the differences between the 46mm S10 Titanium and 49mm U2 - since those are the closest:
1. Dimensions and Weight:
•
Series 10:
• 46mm x 39mm x 9.7mm
• 41.7 grams
• Metal and sapphire crystal back
•
Ultra 2:
• 49mm x 44mm x 14.4mm
• 61.8 grams
• Ceramic and sapphire crystal back
2. Display:
•
Series 10:
• LTPO3 OLED
• 416 x 496 pixels
• 1,220 sq mm display area
• 2,000 nits brightness
• 1.72:1 aspect ratio
•
Ultra 2:
• LTPO2 OLED
• 410 x 502 pixels
• 1,185 sq mm display area
• 3,000 nits brightness
• 1.75:1 aspect ratio
3. Water Resistance and Durability:
•
Series 10:
• Water resistant up to 50 meters
•
Ultra 2:
• Water resistant up to 100 meters
• Depth gauge for diving up to 40m
• Certified to MIL-STD 810H for rugged durability
• EN13319 certification for diving
4. Chip:
•
Series 10:
• S10 SiP (64-bit dual-core processor)
•
Ultra 2:
• S9 SiP (64-bit dual-core processor)
5. Battery Life and Charging:
•
Series 10:
• Up to 18 hours (standard), 36 hours (low power)
• Fast charging: 0–80% in 30 minutes
•
Ultra 2:
• Up to 36 hours (standard), 72 hours (low power)
• Fast charging: 0–80% in 1 hour
6. GPS:
•
Series 10:
• Standard L1 GPS
•
Ultra 2:
• Dual-frequency GPS (L1 + L5)
7. Audio Technology (Speaker and Microphone):
• Series 10:
• Standard speaker for media playback and calls
• Microphone with noise isolation
• Noise monitoring
•
Ultra 2:
• Dual-speaker system (louder output)
• Three-microphone array with wind noise reduction
• Noise monitoring
• Siren (up to 86 dB, audible up to 600 feet)
8. Extra Features (Ultra 2 Only):
• Depth sensor for diving, Siren, Expanded altimeter with a wider range (-500m to 9000m), action button (big one for many too)
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To me it's pretty clear that the S10 chip is just a slightly tuned version of the S9 chip in the Ultra 2, as they both have the same base connectivity (except for the dual-band GPS on Ultra 2), the battery fast-charge time is exactly two times faster on the S10 which makes sense since it's half the rated battery life, so if the chips were the same more-or-less, this would make sense - especially since they're both tested using the same standard 20W Apple charger per the footnotes. The prices for the S10 Titanium are just a tad less than U2 ($749 vs $799) - but for me, the U2 is almost certainly the same chip, has a better battery life by far, and the ceramic casing is a big one among all the other small changes above.
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Will the previous watch bands work with the Apple Watch 10?
Per Apple:
"Older Apple Watch bands, including 41mm and 45mm sizes, will be compatible with the new 42mm and 46mm cases, and all new 42mm and 46mm bands will be compatible with older Apple Watch models" 👍