Battery estimates your charge on a 0 to 100 scale by comparing your recent heart rate variability with your own 60-day HRV baseline. It covers the formula, both Battery settings, the timeline and history, and the sleep and workout markers.
01How Battery is calculated
Titan averages every HRV reading recorded during your smoothing window, which is the last 24 hours by default. It divides that average by your HRV baseline and multiplies by 100. It then multiplies the result by your sensitivity setting, clamps it between 0 and 100, and rounds to a whole number.
Your baseline is the median of your daily average HRV over the last 60 days. Titan needs HRV on at least 7 of those days, and on at least 60% of them, before it will calculate a baseline. Until then Battery stays blank. The 60-day window is fixed and ignores the Recovery window from onboarding, as described in baselines.
At the Default sensitivity, a Battery of 100 means your recent HRV average matches or beats your 60-day median. A Battery of 80 means it sits 20% below that median.
Battery uses the same HRV readings as Recovery. Your HRV method, SDNN by default or RMSSD, and any HRV source set in Data Sources apply to both the average and the baseline. See recovery tools.
02What the status labels mean
The label under the ring on the Battery screen comes from your current charge.
| Current charge | Label |
|---|---|
| 85 to 100 | Charged |
| 60 to 84 | Partially Charged |
| 30 to 59 | Low |
| 0 to 29 | Depleted |
03Smoothing and sensitivity
To change either setting, tap your avatar on Today, then go to You > Settings > Recovery & Sleep > Battery Preferences.
Battery Smoothing sets how many hours of HRV go into the average. The options are 1, 8, 24, 48, and 72 hours. The default is 24 hours. A 1-hour window reacts to each new reading and leaves more gaps, because Apple Watch records HRV only a few times a day. A 72-hour window moves slowly and has fewer gaps.
Battery Sensitivity multiplies the result before Titan clamps it to 100. The right column shows the Battery you would see when your smoothed HRV sits at 70% of your baseline.
| Setting | Multiplier | Battery at 70% of baseline |
|---|---|---|
| Least Sensitive | 0.8 | 56 |
| Default | 1.0 | 70 |
| Higher Sensitivity | 1.25 | 88 |
| High Sensitivity | 1.5 | 100 |
| Maximum Sensitivity | 2.0 | 100 |
At Maximum Sensitivity, any HRV average at half your baseline or higher shows 100. Stay on Default if you want 100 to mean "at my usual HRV".
When you change either setting, Titan deletes your stored Battery history and rebuilds up to 60 days with the new values. The Apple Watch app ignores these settings. It always calculates Battery with a 24-hour window at Default sensitivity, so the watch and iPhone can show different numbers.
04The Battery screen
Tap the Battery card on Today to open the Battery screen. The card shows your current Battery and a 7-day sparkline.
Current charge
The ring shows the most recent point on the timeline that has a value. Under the label, Last observation gives the time of that point. If the timeline has no value yet, the ring falls back to the number on the Today card.
Charge through the day
The timeline covers the 24 hours before now, with one point every 2 hours. Each point uses the same formula, with the smoothing window ending at that point. A window with no HRV leaves a gap, which Titan does not fill. Drag across the chart to read any point. A gap reads "No observation". For a past day, the timeline ends at midnight.
Typical range
The shaded band is your usual charge at the same time of day. It spans the 20th to 80th percentile of the previous 30 days, so the middle 60% of your past values fall inside it. The caption under the chart says how many of the 30 days contributed.
A past day counts only if at least 75% of its timeline points have a value. Titan needs at least 5 such days to draw the band. Each 2-hour slot also needs values from at least 11 days, which is 35% of the window, or that slot stays blank. If fewer than half the slots qualify, the band does not appear.
Sleep and activity markers
Below the chart, the Sleep row draws your sleep session as a purple bar. The Activity row places an icon at the start of each workout that day.
Tap a marker to see its start time, end time, and duration, plus the Start charge, End charge, and Change in points. Titan reports a change only when the timeline has a point within 75 minutes of both ends, no missing points in between, and no gap longer than 150 minutes. Otherwise the marker reads "Insufficient coverage". The change shows what Battery did during the interval. It does not prove the activity caused it.
Daily average charge
The bar chart at the bottom shows one value per day for the last 7, 30, or 60 days. Each bar is the average of that day's 2-hour timeline points, so it can differ from the current charge at the top of the screen. Titan fills missing past days from Apple Health, up to 60 days back.
To recalculate Battery history, go to Settings > Health & Connected Apps > Resync & Troubleshooting and tap Clear Recovery Cache. This also recalculates Recovery, Sleep, and Stress. If Battery stays blank, see HRV not showing.
