Battery & charging
How long a charge lasts, where the power actually goes, and how charging works.
The ZerryBit runs on a 5000 mAh lithium-polymer battery (about 4500 mAh of it usable in practice) and charges over USB-C. Depending on how often it updates, a charge lasts from about three months up to six months and beyond.
Battery life by update interval
These are the estimates the ZerryBit app shows when you pick an update interval, based on our measurements of real devices in normal app use:
| Update interval | Battery life |
|---|---|
| every 10 minutes | ~3 months |
| every 15 minutes | ~4 months |
| every 20 minutes | ~5 months |
| every 30 minutes | 5+ months |
| every 45–60 minutes | ~6 months |
| over 2 hours | 6+ months |
The practical takeaway: pick the longest interval your content allows. A calendar or weather screen rarely needs sub-hour updates, and every step up the table is weeks of extra battery. Frequent intervals make sense for fast-changing content like electricity prices or Home Assistant dashboards.
A press of the Zerry button always fetches fresh content immediately, whatever the interval. The schedule only decides how often the device updates by itself.
Where the power actually goes
The measured numbers behind the estimates:
- Sleep current: ~0.5 mA. The device spends almost all its time in light sleep with the Wi-Fi radio off.
- Battery self-discharge: ~2 % per month (~0.14 mA equivalent), present in every lithium cell.
- A wake-up runs at ~50 mA average. In Self-Host mode on a local network a wake takes about 3 seconds; a normal app-mode wake fetches its images from the cloud over the internet and takes more like 5 to 10 seconds. Most of that time is Wi-Fi and data transfer. The screen refresh itself is a small part.
- Interactive sessions cost more. When you browse widgets, full-screen views, or Settings, the device stays awake the whole time, sometimes minutes. Occasional browsing is fine; it is the automatic schedule that dominates the long-term average.
Because the standing drain (sleep plus self-discharge) never goes away, battery life flattens out at the long end of the table: past an hour or two per update, sleep sets the ceiling.
This is also why the device cannot be woken remotely on demand: listening for a push over Wi-Fi would mean keeping the radio powered continuously, dropping battery life from months to days. Instead the device polls on its schedule, and the button gives you an instant refresh whenever you want one.
Charging
Plug in any USB-C charger. The BQ24074 charger IC fast-charges at about 1 A, so a full charge from empty takes on the order of six hours. The device keeps working normally while charging, it is safe to leave plugged in, and charging terminates automatically when the cell is full.
The sidebar battery icon shows a bolt while charging. A device that lives on the charger will occasionally alternate between the bolt and a full gauge as the charger tops the cell back up; that is the charger's normal maintenance cycle.
About the battery gauge
The percentage is an estimate based on the cell's voltage curve, smoothed over time:
- While charging, the terminal voltage is artificially high, so the gauge deliberately holds its last value rather than showing an inflated number. It settles to the true level shortly after you unplug.
- On battery, the gauge only ever creeps downward between charges. The smoothing prevents sudden jumps in either direction.
When the battery runs critically low, the device shows a "Battery too low" screen and puts itself into a deep sleep that protects the cell. Plug it in and press the Zerry button to bring it back.