🔋 Smart Lock Battery Life Calculator
Enter your smart lock's battery capacity and typical daily usage to estimate how long the batteries will last.
How the estimate is built
Capacity divided by what a day of turning the bolt costs:
days = capacity (mAh) / (cycles per day × mAh per cycle)
months = days / 30
2000 / (8 × 5) = 50 days, about 1.7 monthsMonths use a flat 30 days, so the figure is deliberately blunt. Note what the model contains: motor work, and nothing else. Eight cycles at 5 mAh is 40 mAh a day, which for a Zigbee or Z-Wave lock really is most of the budget, because those radios idle in the tens of microamps.
The standby draw the formula leaves out
A lock is asleep almost all the time, and what it costs while asleep depends entirely on its radio. Typical idle figures:
| Radio | Idle current | Per day |
|---|---|---|
| Zigbee / Z-Wave / Thread | 0.02 - 0.1 mA | 0.5 - 2.4 mAh |
| Bluetooth LE | 0.1 - 0.5 mA | 2.4 - 12 mAh |
| Wi-Fi, always connected | 1 - 3 mA | 24 - 72 mAh |
A Wi-Fi lock therefore spends more electricity waiting than moving. Add 24 mAh of idle to the 40 mAh of motor work and the same 2000 mAh pack lasts 31 days, not 50. Adjust for it by raising the per-cycle figure until the daily total matches.
Frequently asked questions
How long do smart lock batteries last?
On these defaults, 50 days of pure motor use. Real locks vary hugely by radio: a Zigbee or Z-Wave model commonly runs 6 to 12 months on the same cells, while an always-connected Wi-Fi lock is often a two to three month job.
Do four AA batteries give four times the capacity?
No. Cells wired in series add voltage while capacity stays that of a single cell. Enter around 2000-2500 mAh for a four-AA lock, not the sum of the four.
Why do the batteries drain faster in winter?
Two reasons stack. Alkaline chemistry delivers less usable capacity in the cold, and a door that has swollen or dropped makes the motor work harder against the strike, which raises the mAh per cycle you should be entering.