Power an Old Phone Without a Battery

My much-loved 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 see if we can remove it and power it straight from USB.

An Old Phone

XL4015 Buck Converter

USB-C Power Delivery Trigger Module Board

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 3.7V to 4.2V depending on the state of charge. By removing the cell, we can supply our own power source within this range, and the phone should boot.

Set the Power Delivery trigger module to request 9V from the source, and connect it to the input side of the buck converter. Then connect the output side to the battery PCB, making sure to get the polarity right.

Remember to adjust the buck converter to output 4-4.2V!

Connect a compatible power bank or charger and power the phone up! It should boot without an issue.

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