Battery life

When transmitting data, an nrf52840 dongle consumes around 1000 uA (1mA) In sleep mode, it consumes 20 uA. A Good coin cell battery can have around 200 mAh. So sleep battery life. 200mAh/20uA = 10000 hrs in deep sleep mode. 10000hrs > 416 days > a bit more than a year.

In transmitting: - Single press activates advertising, and if there is no next activity for half a second then advertising turns off. - So we have a consumption of 1mA during half second for a single press. So about Coin cell has 200 mAh -> 200 * 3600 mAsec or 7200 single presses.

How long will then a average coin cell battery last in sleep mode only?

• 500 mAh / 0.02 mA = 25,000 hours ≈ 1,042 days or about 2.85 years How long will the battery last in active mode only?

• 500 mAh / 1 mA = 500 hours ≈ 20.83 days”

But in general, cheap batteries will have less capacity.

If we have a 1000 mAh battery/ 0.02 mA = 50,000 hours ≈ 2,083 days or about 5.7 years sleep mode. Active mode only: 1000 mAh / 1 mA = 1000 hours ≈ 41.67 days

In our real world tests this stands up. We had our code running actively (a switch press per second) We calculated 3392945 switch presses in a total of 809hours approx 33 days. It was still going and we decided to read its battery voltage where we read 3.7. It starts at 4.2.

How does this compare with HID?

2532 uA (2.532 milliamperes) constant draw is seen on an HID connection with an nrf52840. So it consumes more than 2.5x more power.