Powering an Arduino with a power bank

Can you power an Arduino with a USB power bank? Yes, but there’s a catch: many power banks turn themselves off after a few seconds, because the Arduino draws so little current that the power bank thinks nothing is connected.

Here’s how I found out.

I was working on an Arduino project and when I finished it I said “well it’d be cool to power it with a USB power bank and put it outside”.

I did that. I connected the Arduino to the power bank and it worked!

But after about 20 seconds the Arduino powered off.

Well, the power bank turned off. And along with it the Arduino.

Why does the power bank shut off?

Power banks are built for charging phones. A phone charging pulls a lot of current, often 1A or more.

To save their own battery, power banks monitor how much current is flowing out. When it drops below a threshold, they assume the device is done charging, or that nothing is plugged in, and they cut the power. The exact threshold depends on the model, but it’s usually far more than an Arduino needs.

An Arduino board running a sketch draws only a few tens of milliamps. From the power bank’s point of view, that looks like an empty port. So it waits a handful of seconds, then shuts off.

The frustrating part is that everything works at first, so you think the problem is your code or a loose cable. It’s neither. The board is fine.

The possible fixes

I found some solutions to the problem, involving making the Arduino consume more power, like periodically driving a load so the total current stays above the power bank’s cutoff threshold. This one describes the approach: https://www.instructables.com/USB-External-Battery-Packs-on-Arduino-turns-OFF/.

It works, but you’re burning battery on purpose, just to keep the power bank awake. For a project meant to run outside for days, that felt wrong.

Another option is getting a power bank that doesn’t turn off automatically. Some models have an “always on” or trickle-charge mode made for low-power devices like fitness trackers. If you already own one, check for a button combination that enables it.

What I did instead

In my case I decided to go with a rechargeable battery instead, since I was working with an Arduino MKR 1010 WiFi and it had a 3.7V Li-Po battery option.

The board has a battery connector and a built-in charging circuit, so the battery charges whenever the board is plugged into USB, and takes over when you unplug it. No minimum current requirement, no surprise shutdowns.

If your board supports a battery directly, that’s the cleanest way out of this problem.