Power

A solar cell or photovoltaic cell is a device that converts light directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make [...]

Here are some basic data (size, capacity) of various chargeable, non-chargeable batteries.

Regulators are simple and cheap way to create 5v or 3.3v (or any desired voltage if it is made for it) Often when you use a microcontrollers (i.e. arduino) or a wireless communication module (i.e. xbee, bluetooth), you need to supply exact voltage the device requires. This is an example of sewable 3.3v regulator and 9V battery [...]

from Wikipedia: also: Lithium-ion polymer batteries, polymer lithium ion, Li-poly, Li-Pol, LiPo, LIP, PLI or LiP Rechargeable batteries which have technologically evolved from lithium-ion batteries. Ultimately, the lithium-salt electrolyte is not held in an organic solvent as in the lithium-ion design, but in a solid polymer composite such as polyethylene oxide or polyacrylonitrile. The advantages [...]

There is an interesting tutorial for how to make 3V step-up circuit by using simple component from. The project is called Joule Thief. With this module, you can light up LED (it needs 3V) with single AAA battery (1.5V).

These neoprene battery pouches are made to fit different kinds of common batteries. They turn out to be very useful when prototyping and competing a range of different projects, not necessarily just wearable ones.