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Garmin · Body Battery
Body Battery is the most-checked Garmin metric on a typical day — and the most often misinterpreted. Athletes look at the number, assume it means 'how tired I feel right now,' and stop there. The actual signal is more useful and more specific than that.
Body Battery is Garmin's proprietary blend of HRV (heart rate variability), perceived stress, sleep, and activity load. It updates continuously, so it answers a different question than Training Readiness (daily) or Training Status (multi-week). Body Battery tells you what your autonomic nervous system has been doing this morning.
| Above 75 | Fully recharged. Ideal state for a quality session — intervals, threshold, race-pace work. If you're consistently waking above 75, your recovery is well-aligned with your load. |
|---|---|
| 50–75 | Moderate. Suitable for normal training, including most aerobic runs. You can train but probably shouldn't add a maximal effort. |
| 25–50 | Below average. Treat today as recovery or easy aerobic. A quality session here is more likely to feel hard and produce less adaptation than the same session at 70+. |
| Below 25 | Depleted. You should rest, do active recovery, or run very easy. If you wake here repeatedly, your load is too high for your recovery — and Training Status will turn Unproductive within a week or two. |
| Drops during the day | Normal — Body Battery falls with activity, stress, and time awake. A 20–30 point drop during a hard training session is expected. A 40+ point drop on an easy day suggests stress, illness onset, or under-fueling. |
| Recharges overnight | Sleep is where Body Battery climbs. Poor sleep architecture (lots of light sleep, little deep or REM) recharges less. A 6-hour night of mostly light sleep can produce a worse Body Battery rebound than a 5-hour night with deep sleep. |
Garmin doesn't publish the exact formula, but reverse-engineering and confirmed inputs show it's a weighted blend of: HRV (heart rate variability) — the dominant signal; perceived stress (also Garmin-derived from HRV); sleep duration AND sleep architecture; activity load; passive recovery (low-stress periods during the day).
This is why Body Battery moves throughout the day, while HRV is essentially a one-shot overnight number. A long stressful meeting, even seated, can drop your Body Battery 15–25 points. A walk in the sun with no exercise can raise it 5–10 points.
Newer Garmin devices (Forerunner 265/955/965, Fenix 7/8, Epix) compute Body Battery with the latest Firstbeat algorithm and tend to be more accurate than older devices. Wrist contact and band tightness affect HRV detection — if your numbers seem off, check the strap fit before blaming the metric.
Daily timing of stress: HRV is a single morning snapshot. Body Battery shows you when stress accumulated during the day — useful for spotting that a particular meeting, commute, or evening workout is wrecking your recovery curve.
Sleep architecture quality: if you slept 8 hours but Body Battery only rebounded 30 points, your sleep wasn't restorative. Look at the sleep stages screen — usually low deep sleep or low REM is the cause.
Acute illness or stress onset: an unexplained drop of 15–25 Body Battery points without matching exercise or sleep loss is often the first signal of brewing illness or accumulated under-fueling.
Wake-up reading: this is the most useful single read. Above 75 → today supports a hard session. 50–75 → normal aerobic. Below 50 → easy day or rest.
Pre-workout reading: if Body Battery has dropped 15+ points since waking and you haven't trained, your day was stressful. Lower the planned intensity.
Post-workout reading: a hard session should drop Body Battery 25–40 points. A drop bigger than that for the same session over multiple weeks is a sign of accumulated fatigue.
Weekly pattern: if your morning Body Battery is trending down across the week, you're not recovering between sessions. Add a deload week.
Sleep duration matters less than sleep architecture. If you slept 8 hours but most of it was light sleep, recovery was poor. Other causes: heavy meal late at night, alcohol (even one drink dramatically suppresses HRV-based recovery), high stress entering sleep, illness in early stages.
100 is rare and requires unusually high HRV + long deep sleep + low cumulative stress. Athletes in heavy training don't usually hit 100 — that's normal. Worry about whether the wake-up number is improving week over week, not whether it reaches a specific ceiling.
Yes. Common cases: bad wrist contact during sleep (loose band) reduces HRV detection accuracy; recent device change (algorithm differences); medications affecting HRV (beta-blockers especially); long-haul flights for ~3 days; menstrual cycle phase (luteal phase often shows lower Body Battery despite same fitness).
Easy aerobic running below 70% MaxHR is almost always fine, even at low Body Battery. Quality sessions (intervals, threshold, long-tempo) at low Body Battery produce poor adaptation and increase injury risk. Move quality to a higher-Body-Battery day.
Both are HRV-based readiness scores. Body Battery updates continuously and shows time-of-day patterns; Whoop is once-daily and weights HRV more heavily. Body Battery is better for in-day decisions; Whoop Recovery is a cleaner single-shot morning signal. Neither is more accurate — they measure overlapping signals slightly differently.
CoachUpFit reads your morning Body Battery and HRV together — if you're under-recovered, today's session auto-adjusts before you see it. Free for 7 days, then $20/month.