If you're looking for a simple way to add a battery to your LilyPad project, the LilyPad Coin Cell Battery Holder might do the trick. It's a simple board which holds a 20mm coin cell battery (such as a CR2032) and gives you 4 connection points (two positive and two negative) for sewing into your project. Project description, more information and ordering can be found at https://www.sparkfun.com/products/10730