Garmin vs COROS: the solar lens against the biggest battery without one

The verdict

These two brands have genuinely different theories of what a long-lasting watch is, and both are defensible.

COROS makes the battery enormous. The VERTIX 2S is quoted at 36 days of daily use, 118 hours of standard full GPS, 73 hours with all systems on and 43 hours dual-frequency, in a sapphire-and-titanium case at 10 ATM. Nothing from Garmin matches that GPS figure without the sun helping.

Garmin removes the charging problem instead. The Instinct 3 Solar is rated up to 40 days of typical use and unlimited smartwatch battery with three hours a day at 50,000 lux, plus up to 260 GPS hours with solar. The fenix 8 Solar 51 mm does 30 days, 48 with solar, 95 GPS hours and 149 with solar.

On this site the second approach wins, for a reason that has nothing to do with the headline numbers: a rechargeable lithium cell ages by charge cycle, so the watch that cycles six times a year is the watch still worth wearing in 2036. A 36-day watch charges about ten times a year. A solar Instinct worn outdoors may never charge at all. That is the argument, and it is laid out at length in buy-it-for-life watches.

Battery, in both makers' tables

No estimates here: these are the figures each maker publishes, which is also why the modes are named differently. COROS quotes standard full GPS, all systems and dual-frequency; Garmin quotes GPS-only, max-battery GPS and expedition mode, each with and without solar.

Read it in two columns rather than as a race. In pure numbers with no sun, COROS wins the GPS row outright: 118 hours of standard full GPS on the VERTIX 2S against 60 GPS-only hours on the Instinct 3 Solar and 95 on the 51 mm fenix 8 Solar. Add sunlight and Garmin's numbers go to 260 and 149 hours respectively, and its smartwatch row stops having a number at all.

Which column is the real one depends entirely on whether your watch sees daylight. For a hunter, a rancher, a thru-hiker or anyone working outside, the solar column is the honest one. For someone who trains outdoors and works indoors, COROS's raw figures are closer to what you will see.

The solar question, which is the whole argument

COROS does not sell a solar watch. That is not a criticism of the engineering; it is a product-line fact with a consequence.

A solar lens does two things. The obvious one is extending runtime, and that is what the marketing talks about. The one that matters over ten years is that it keeps a lithium cell near the top of its charge without plugging in, which reduces the number of full cycles the cell sees. Cycle count, not calendar age, is the dominant factor in how much capacity a lithium cell has left. A watch with half its original capacity in year eight is a watch you replace.

So the comparison is not 118 hours against 60. It is 118 hours against a watch that may still be at most of its original capacity when the COROS has been through 80 or 100 full cycles. The mechanism is explained in Garmin solar explained and the practical routine in how to charge a solar watch.

Materials and water rating

COROS is unusually generous here and Garmin is unusually careful, so read both makers' words exactly.

The VERTIX 2S specifies sapphire glass with a Grade 5 titanium alloy bezel and a titanium alloy cover, at 10 ATM, which COROS qualifies as surface water activities and not diving. The NOMAD drops to hardened mineral glass, a fibre-reinforced polymer case with an aluminium alloy bezel and 5 ATM.

The Instinct 3 Solar is a metal-reinforced bezel on a fibre-reinforced polymer case, 10 ATM, and Garmin describes the display only as scratch-resistant, which is why we do not flag it as sapphire. The fenix 8 Solar is the one that beats everything here: a sapphire lens, a titanium bezel, leakproof metal buttons, a metal sensor guard and a case Garmin dive-rates to 40 metres rather than simply water-rating.

Two things fall out of that. If you want sapphire cheaply, COROS is the answer and Garmin is not. If you want a case rated for actual diving, Garmin is the answer and COROS explicitly is not. The ranking of lens materials across the whole site is in most scratch-resistant smartwatch.

One more Garmin-only line worth weighing: both Garmins here are built to MIL-STD-810 for thermal and shock resistance, in Garmin's own words. COROS makes no MIL-STD claim on these models, so we do not flag one. What the standard does and does not promise is in MIL-STD-810 watches explained.

Weight and size

COROS publishes its weights twice, once on silicone and once on nylon, which is a genuinely useful habit. The VERTIX 2S is 87 grams on silicone and 70 on nylon, at 50.3 by 50.3 by 16 mm. The NOMAD is 61 grams on silicone and 49 on nylon, at 47.8 by 47.8 by 14.8 mm, which makes it one of the lightest mapping watches anyone sells.

If weight is your deciding factor, the NOMAD is a strong answer and the strap swap is worth knowing about on any watch; it is the cheapest comfort upgrade there is, as covered in resin vs steel cases.

Where you can actually buy them

This is the practical difference nobody writes about, and it matters for a watch you intend to own for a decade.

The VERTIX 2S has no Amazon listing at all. We checked the catalogue directly and the model is not sold there; the buy link on this site is an honest tagged search rather than a product page we invented. COROS sells it directly, and the NOMAD is on Amazon normally. Garmin's entire line is on Amazon, at every retailer, with a used market, third-party straps and independent repairers.

For a buy-it-for-life purchase, distribution is part of serviceability. The brand whose bands, bezels and batteries will still be obtainable in year eight is the brand with the bigger installed base, and that is Garmin by a wide margin.

Who should buy neither

If what you want is a watch with nothing to charge ever, both of these are the wrong category. A Casio Tough Solar ABC watch runs for months in the dark on its reserve, costs a fraction as much, and has no software to go unsupported; the options are in best ABC watches and best Casio Pro Trek.