Make a 5 volt battery supply for any Arduino

Powering your Arduino from a 9v battery and the built-in linear regulator is inefficient; 9v batteries have very low energy capacity, and
using a simple linear regulator (perhaps 60% efficient) wastes much of it. 9v batteries are also quite expensive compared to other battery types.

A switching regulator can be over 95% efficient. 14500 Lithium cells, which are the same size as AA cells, but deliver 3.7v each, are much more cost effective in the long term than disposable alkaline cells.

This project shows you how to make a regulated 5v supply that is about the same size as a 9v battery, and which you can connect direct to the 5v pin (NOT the power socket, nor the VIN pin) of your Arduino or other circuit.

Gather the parts

The core of the circuit is this regulator module which will take up to 23v in and output from 1 to 17 volts depending on adjustment (as long as the input is higher than the desired output). It costs less than a single 9v battery.

You also need a battery snap, some heat-shrink tubing, and a battery of some kind. I recommend a 2xAA holder holding two 14500 lithium cells, which are rechargeable 3.7v Lithium Ion cells and cost less than $5 a pair.

Assemble the parts

Begin by selecting some heat-shrink tubing of the appropriate size, and punching two holes for the battery connectors.

Then cut and solder the battery snap wires to the regulator.

Connect the regulator and adjust the trimming potentiometer with a small screwdriver until the output reads 5 volts. Disconnect battery.

Fit the heatshrink over the battery snap, then feed the battery snap wire and the regulator module into the heat shrink.

Use a heat source to shrink the tubing. You don't have to be obsessive, just shrink until snug.

Use your assembled battery

A handy tip for when working with 9v battery snaps, when you need to switch on and off, just connect ONE pin, and rotate the snap until the snap makes contact with the outside of the other pin to turn on. You can rotate the snap to bring the pins apart to switch off.

Remember, you have your own high-efficiency low-dropout regulator, so you do not need to use any regulator built into your Arduino, you can connect direct to the ground and 5 lines.