Over the last decade or so, battery technology has improved massively. While those lithium cells have enabledthin, powerful smartphones and quadcopters, [patrick] thought it would be a good idea to do something a littlesimpler. He built a USB power bank with an 18650 cell. While it would be easier to simply buy a USB power bank,that’s not really the point, is it?

This project is the follow-up to one of [patrick]’s earlier projects, a battery backup for the Raspberry Pi. This earlierproject used an 14500 cell and an MSP430 microcontroller to shut the Pi down gracefully when the battery wasnearing depletion.

While the original project worked well with the low power consumption Pi Model A and Pi Zero, it struggled withUPS duties on the higher power Pi 3. [patrick] upgraded the cell and changed the electronics to provide enoughcurrent to keep a high-power Pi on even at 100% CPU load.

The end result is a USB power bank that’s able to keep a Raspberry Pi alive for a few hours and stays relativelycool.