Powering LilyPad LED Projects
Gella , 
MikeGrusin 
How Long Will My Project Run on Battery Power?
To figure out how long your project will run on battery power, you need to know two things: how much current your project uses and the capacity of your battery.
You can measure exactly how much current your project uses by measuring it with a multimeter, but we can also make a pretty accurate guess by looking at the LED datasheets and doing some math.
A typical LilyPad LED uses 20mA of current at full brightness. Multiply that by the number of LEDs you’re using, add 10mA for the LilyPad that’s running everything, and you’ll have an estimate of your average current draw.
A project with 10 LilyPad LEDs controlled by a LilyPad Arduino
20mA * 10 + 10mA = 210mA
A single LilyPad Pixel Board will use 40mA when it’s set to white (all three internal LEDs fully on). For a worst-case estimate, you could multiply that by the number of pixels in your project.
However, you’ll probably be displaying different colors on your LilyPad Pixel Boards and turning them off entirely at times. The resistance in the threads will also drop the voltage, meaning the LilyPixels will run slightly dimmer and use less current. Usually, it’s safe to halve the above estimate, which gives us 20mA.
For more detailed information on working with LilyPad Pixel Boards, take a look at our LilyPad Pixel Board Hookup Guide.
Battery Capacity
Now, let’s look at the battery. Battery capacity is given in milliamp-hours (mAh). This number tells you how many milli-amps (mA) a full battery can provide for one hour before it’s empty. The e-Textiles Battery that comes with most LilyPad Arduino kits has a 110mAh capacity. For many projects, especially ones with a large number of LEDs, you will probably want to use a higher capacity battery for a longer run time.
Hours = Battery mAh / Project mA
Let's use the calculation above to see how long a 110mAh battery will power the project we used in the last example:
0.52 hrs = 110mAh / 210mA
Thus, an e-Textile battery will only power the project for approximately half an hour. Here's an instance where a larger capacity battery would make sense, if the project needs to operate for a long time, such as during an event or showcase. The trade-off is that a higher capacity battery is also physically larger -- make sure to plan accordingly for proper battery storage/attachment on your project to reduce strain on the wires and fabric.
Here are some typical runtimes for various SparkFun batteries and numbers of LilyPad LEDs/LilyPixels:
| Number of LEDs | 1 | 2 | 5 | 10 | 20 | ||
| Battery Name | Battery mAh | Hours of Operation | |||||
|---|---|---|---|---|---|---|---|
| Polymer Lithium Ion Battery - 40mAh | 40 | 1.3 | 0.8 | 0.4 | 0.2 | 0.1 | |
| E-Textiles Battery - 110mAh (2C Discharge) | 110 | 3.7 | 2.2 | 1.0 | 0.5 | 0.3 | |
| Coin Cell Battery - 20mm (CR2032) * | 250 | 8.3 | 5.0 | 2.3 | 1.2 | .61 | |
| Polymer Lithium Ion Battery - 400mAh | 400 | 13.3 | 8.0 | 3.6 | 1.9 | 1.0 | |
| Polymer Lithium Ion Battery - 850mAh | 850 | 28.3 | 17.0 | 7.7 | 4.0 | 2.1 | |
| Polymer Lithium Ion Battery - 1000mAh | 1000 | 33.3 | 20.0 | 9.1 | 4.8 | 2.4 | |
| Polymer Lithium Ion Battery - 2000mAh | 2000 | 66.7 | 40.0 | 18.2 | 9.5 | 4.9 | |
| Polymer Lithium Ion Battery - 6Ah | 6000 | 200.0 | 120.0 | 54.5 | 28.6 | 14.6 | |
* Note: the Coin Cell Battery is non-rechargeable.