This Lilypad LiPower is pretty cool.
It’s basic role is to convert a 3.5v Lythium Polimer battery to 5v for Powering an Arduino micro-controller. That is done with the + and – pins in the bottom half of my photo.
Additionally it has a connection for charging the battery without disconnecting it or removing it from the project. That is done with the (partially obscured) c and – pins toward the top of my photo.
Also toward the top is a switch that turns the power to the Arduino on and off. The battery charges regardless of this switches position. This LiPower is inside the project I am working on, so I’ve added an external switch (SPST) by connecting it to two of the pins of the on-board switch.
So far this set-up is working fine. I can plug a charger externally and switch the Arduino’s power while the battery is charging or not.
UPDATE: Since writing this, I have added a connection between the B pin on the Lipower board to an analog pin on the Arduino. By doing this I can now read the voltage of the battery and light a warning LED when it gets low. I found that the Lipower outputs 5v until the battery voltage drops below about 2.9v. At that point the Lipower switches things off to protect the battery.