Body Battery explained

Body Battery is a 0–100 index of your current energy reserve. It tracks relative energy, not an absolute physical amount. It rises during rest and sleep and falls during activity, stress, and strain.

Battery bands

The app groups Body Battery into three bands:

• High: 65 and above
• Medium: 35 to 64
• Low: below 35

A High value means you have plenty of reserve. A Low value is a prompt to prioritise recovery.

Phases

Body Battery moves through three phases:

• Charging: the index is rising, typically during sleep, naps, or quiet rest.
• Draining: the index is falling, usually during activity, mental stress, or sustained exertion.
• Stable: the index is flat, meaning inputs and drains are roughly balanced.

The phase depends on the recent rate of change, not the absolute number.

Triggers

The app tags the most recent driver of a Body Battery change so you can see what moved the needle. Trigger tags include:

• sleep: overnight recharge
• activity: movement and exercise
• stress: sustained autonomic load
• rest: quiet recovery such as reading or meditation
• illness: a stress-like pattern sometimes seen when you're feeling under the weather
• jetLag: recent travel across time zones

A single trigger does not determine the score. It simply explains the latest shift.

How it is calculated

Body Battery is modelled as a leaky integrator that continuously balances HRV-derived stress, activity load, and rest. The model runs on the device and updates through the day as new data arrives.

Using Body Battery

• Use High periods for demanding tasks or harder training.
• Use Low periods for lighter movement, sleep extension, or recovery-focused habits.
• Track the shape of your curve over days, not just the current number.