I am supplying power to a Arduino Uno that draws 45mA of current and a sensor that draws 20mA with a 9 Volt battery(ampere for battery is 550 mAh. How much power is the whole system consuming?

I am also trying to figure out how long the 9 Volt battery will last. I added the currents together and divided that by 550 which resulted in 8.46 hours, but I am not sure that is correct.

  • \$\begingroup\$ That depends on the circuit. There are a couple of ways you can hook up what you're describing. Perhaps the sensor is connected across the terminals of the battery, perhaps the sensor is connected to the terminals of the Arduino (5 V + Ground). Who knows? \$\endgroup\$ Commented Dec 1, 2018 at 7:36
  • \$\begingroup\$ If the Arduino supply is 5V derived from the 9V using a linear regulator, you can try to save power by switching to an SMPS DC-DC converter. \$\endgroup\$
    – Oldfart
    Commented Dec 1, 2018 at 8:13
  • \$\begingroup\$ Your answer is correct but you got it by dividing "into 550" and not "by 550". \$\endgroup\$
    – Transistor
    Commented Dec 1, 2018 at 8:25

1 Answer 1


if those figures are correct, that result is correct.


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