Will my GPS watch last a 100-mile ultra?

Most modern GPS watches last 20-30 hours in full GPS mode. A 100-mile ultra taking 24-36 hours will need UltraTrac mode or expedition mode to last. Alternatively, carry a lightweight power bank and charge on the move.

How does cold weather affect GPS watch battery?

Cold temperatures reduce lithium battery capacity significantly. Below 5°C, expect 2-3% battery loss per degree. At -10°C, you may lose 30% of total capacity. Keep the watch under your sleeve in very cold conditions.

What is UltraTrac mode?

UltraTrac (Garmin) or equivalent modes reduce GPS recording frequency from every second to every 30-60 seconds. This roughly triples battery life but reduces track accuracy. Acceptable for ultra races where exact GPS tracks are less important.

Does optical heart rate monitoring drain much battery?

Optical HR uses the green LED sensor and typically reduces GPS battery life by about 10%. For very long races, using a chest strap and disabling optical HR can save meaningful battery. Music streaming has a much larger impact at 25-35% extra drain.

RunCalcs

GPS Watch Battery Calculator — Ultra Race Planning

Calculate if your GPS watch battery will last for ultra-distance races based on mode and features.

GPS ModeGPS recording frequency

Features EnabledActive features during the race

Race Duration

Expected time to finish the race

Expected Temperature

Average temperature during the race

How We Calculate This

Battery Estimation

Battery hours = Base hours x Feature factor x Capacity factor x Temperature factor x Backlight factor

Base Battery by GPS Mode

Full GPS (1s): ~20 hours
Smart recording: ~30 hours
UltraTrac: ~60 hours
Expedition: ~120 hours

Feature usage, cold temperatures and backlight reduce available battery. The default 20h base can be adjusted to match your specific watch model.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always consult a coach or medical professional for personalised training advice.