Let's face it, 9V batteries suck.  They don't last long, they're expensive, and did I mention they don't last long?  I work on and run several electric RC cars, and because of  this I own a lot of Lithium Polymer (LiPo) batteries.  Nowadays you can get them for pretty decent prices, and if you know how to take care of them (don't ever use them if you don't) they'll last you a long, long time.

While your average pile alkaline 9V has a capacity of about 565mAh and costs somewhere around $2, a budget 2S (7.4V) LiPo pack that costs $9 can have a capacity of 1800mAh, with the bonus of 1,000+ charge cycle capability.

To use my LiPo packs on my Arduino, I made a simple adapter from Deans Ultra (the type of plug I have soldered onto all my LiPos) to the barrel plug that fits into the Arduino.  Make sure that when you use a LiPo for an extended period of time, or any time at all for that matter, always connect it to a low-voltage cutoff (if your LiPo drops below 3.0V per cell, you're pretty much dead in the water).

Now I can run my Arduino away from the wall or computer for long periods of time and for a low cost, and you can, too!

If you think this is a good tip, please vote for this Instructable in the Electronics Tips and Tricks contest!  The vote button is in the top right of this Instructable, right above the title. Thanks!
retrolefty says: 9 months ago
Yes in this day and age there makes little sense to use batteries to drive linear regulators. Here is a simple DC/DC switching regulator that could take this Li-po
battery voltage and regulate it to +5vdc for direct connection to the arduino 5V pin
or better yet hack a old spare USB cable, lop off the PC end and connect the ground
and positive wires, connect to regulator output and plug into arduino's USB connector.

Lefty says: 1 year ago
Running a 9V battery through a 5V linear regulator (as on the arduino), wastes 44% of the battery power right off the top (4V of that 9V gets turned into heat, which is why the regulator gets so hot). Linear regulators are terrible for running off battery. Their main advantage is they are cheap and provide a very clean output voltage.
Radioactive_Legos (author) in reply to davr.org1 year ago
Good point! The batteries I use here are 7.4V nominal, so the drop is lower. The main purpose of this Instructable is to demonstrate how Lithium Polymer batteries can be integrated into an Arduino project for longer runtime and lower cost in the long run.
maninvan in reply to Radioactive_Legos1 year ago
I would recommend running a non-linear BEC with 5V output and power the Arduino using the 5V input pin to be more efficient. Even if you burn 33% in heat that's 700mAh compared to the 175mAh on my 9V NiMH battery :-o

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