Battery Reality Gap · Comparison
Garmin Fenix 8 vs Coros Vertix 2S
Forensic battery comparison · Formula v1.0
On paper this is not close: Garmin prints 84 hours for the Fenix 8, Coros prints 43 for the Vertix 2S. The Fenix claims nearly double. Under the HikingSpecs reference scenario the result inverts. Formula v1.0 calculates the Vertix 2S blacking out at 22.96 hours and the Fenix 8 at 19.9. The watch that advertises half the endurance survives three hours longer on the route that matters, and it costs two hundred euros less. This is what happens when you measure physics instead of reading the box.
How the smaller claim wins
Two physical properties decide it. The Vertix 2S carries a 2618 mWh cell against the Fenix 8's 2400, more usable energy before any penalty lands. More important is the case: the Fenix 8's titanium body is an efficient thermal conductor that bleeds the cell's heat to ambient under wind-chill, dropping the core temperature into the range where lithium-cobalt capacity collapses. The Vertix 2S uses a polymer body with titanium only at the bezel and backing, so it retains that heat and the Arrhenius penalty lands softer. Garmin's marketing number is built on a warm, idle bench; the mountain erases the gap.
Both still fail their claim
This is not an endorsement of the Coros as a safe planning tool. The Vertix 2S posts a 46.6 percent Reality Gap and the Fenix 8 a 76.4 percent gap, and both carry a CRITICAL classification under the reference scenario. Neither watch lasts its advertised hours under cold, multi-band, continuous GPS. The point is narrower: between these two, the cheaper watch with the smaller printed claim is the one that fails later, and the premium titanium build is the reason the expensive one fails first.
The verdict
At €699 against €899, the Vertix 2S is cheaper and lasts longer under the reference scenario, which makes it the more rational endurance buy of the two despite the smaller marketing claim. The Fenix 8 wins on display, mapping, and ecosystem; it does not win on the metric this lab measures. Read the full forensic breakdown in the Vertix 2S dossier or the Fenix 8 dossier.
Physics-derived estimate under one fixed reference scenario. The model is calibrated but not yet independently validated against measured field runtime. Estimated hardware inputs are labeled as such. Full method at /methodology.