Between the T-Rex 3 and Fenix 8 (47mm), the T-Rex 3 comes out ahead in peak brightness and battery life, while the Fenix 8 (47mm) wins on ecg. Overall, the T-Rex 3 scores 79.7 and the Fenix 8 (47mm) scores 64.3 on our Mars Score.
Which should you buy?
The T-Rex 3 is the clear pick on raw spec strength, leading by 15.4 points on the Mars Score. The margin is wide enough that the underdog only makes sense if its individual strengths line up with what you specifically need.
Pick the T-Rex 3 if your top frustration with your current device is running out of charge before the day ends — endurance is the lead spec here. The biggest gaps in its favor are peak brightness, battery life, display size, among others.
Pick the Fenix 8 (47mm) if you care most about ecg. Its strongest claims are ecg.
Both ship with comparable cellular, spo2, water resistance, so those specs don't separate the two — focus on the differences below.
Bottom line: the T-Rex 3 is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Why Amazfit - T-Rex 3 wins
- ▲Peak brightness — 100.00% more. 2000 nits vs 1000 nits.
- ▲Battery life — 75.00% more. 672 h vs 384 h.
- ▲Display size — 7.14% more. 1.5 " vs 1.4 ".
- ▲Weight — 5.00 g less. 68 vs 73.
Why Garmin - Fenix 8 (47mm) wins
- ▲Has ECG.
Spec comparison
Design
| Spec | Amazfit - T-Rex 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Case size | 48.5 mmlead | 47 mm |
| Weight | 68 glead | 73 g |
| Case material | polymer | fiber-reinforced polymer |
| Water resistanceⓘ | 10 ATM | 10 ATM |
Display
| Spec | Amazfit - T-Rex 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Display size | 1.5 "lead | 1.4 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 2000 nitslead | 1000 nits |
Health & Fitness
| Spec | Amazfit - T-Rex 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| ECG | false | truelead |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Amazfit - T-Rex 3 | Garmin - Fenix 8 (47mm) |
|---|---|---|
| Battery life | 672 hlead | 384 h |
| GPS | true | true |
| Cellular | false | false |
| NFC | false | truelead |
| OS | Zepp OSlead | Garmin OS |
Frequently asked
Which has longer battery life, T-Rex 3 or Fenix 8 (47mm)?+
T-Rex 3 lasts 672h vs 384h.
Do T-Rex 3 or Fenix 8 (47mm) support ECG?+
Fenix 8 (47mm) supports ECG; T-Rex 3 does not.
Which has cellular, T-Rex 3 or Fenix 8 (47mm)?+
Neither offers cellular.
Spec-level deep dives
More from the same brands
vsMars is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you. Learn more.