Power a Phone Without a Battery

My old Pixel 3a has been sitting in a drawer gathering dust for a while now, which feels like a bit of a shame. Why buy a Raspberry Pi for a project when I already have a more capable device lying in a drawer?

There’s one problem: unless you like a spicy pillow, leaving an old phone plugged in 24/7 probably isn’t the greatest idea. Let’s remove it and power it straight from a USB power source.

1. An old phone
2. XL4015 buck converter
3. USB-C Power Delivery trigger module
4. Power bank or charger that supports power delivery

Follow a guide to disassemble your model of phone and remove the battery. For my Google Pixel 3a, this iFixit guide was helpful.

The battery consists of two parts: the bare cell; and a long, thin circuit board that protects and monitors it. Remove the sleeving and desolder the board.

This board expects to see a voltage roughly between 3V to 4.2V depending on the state of charge. By removing the cell and supplying your own power source within this range, the phone will be able to boot.

Set the Power Delivery trigger module to request a higher voltage from the source (I used 9V), and connect it to the input side of the buck converter.

Before connecting it to the phone, adjust the buck converter to output around 4 to 4.2V.

Then connect the output side to the battery PCB, making sure to get the polarity right.

Add an extra wire from the negative tag of the battery PCB and ground it to the chassis of the phone. In this case I tucked it under the screw holding the USB-C port in place.

Without this the phone may not boot.

Reassemble the phone and connect a power bank or charger that supports USB Power Delivery to the buck converter. The phone should boot without an issue!

You can check out my YouTube Channel for more interesting projects, or visit my website for more information!