Lithium-ion battery pack
Lithium-ion battery packs are common components in portable electronics and tools today. Many of these batteries have not exhausted their useful life when they are discarded, and are rather easy to re-use in new projects. There is a large amount of information out there about their use, and many projects that incorporate them. This page for now will explain a cheap and simple way to turn a recovered "cell", or single battery, into a USB charging device, for a low cost.
To achieve this you will need a Rechargable Lithium-Ion battery. A name that's often used for a specific size of battery that is very common is an 18650 battery. Batteries will come in many shapes and sizes, however the 18650 battery due to it's ubiquity is well catered for, in terms of this project, when it comes to available 3D printed mounts.
Along with the battery and an optional mount, you'll want one, or two optional electronic components, depending on what you'll use it for. The mandatory component is a protection circuit board for safely charging the battery. Some battery cells have boards attached already, often hidden within a heatshrink plastic wrapper. An example of one of those boards can be seen in the image to the right. If you don't have one of these circuits, you can buy a "Tp4056" module from online marketplaces such as Aliexpress for a dollar or so. Once you have one of these, and you've wired it up, it's possible to charge the battery safely, and to use that charge. However, the power output will vary in voltage as the battery loses charge. If you need to power USB type devices, this will likely not be satisfactory, so you may need to get a "5v Step-Up Voltage Regulator". These again can be found on online marketplaces for around $1.