Powerbank module 134n3P / 1S 18650

thingiverse

This tiny device takes one of those affordable eBay power bank modules "134N3P" and clips onto a 18650 battery holder. By doing so, you can get a compact power bank made from just one 18650, all at an incredibly low cost under $1. My trusty 18650 is actually salvaged from an old laptop battery that's been repurposed for this project. The electronic module seems to be robust enough not to shut down below the 20mA threshold. As a result, this power bank makes an ideal portable power source for Arduino and ESP8266 projects alike.