1. *http://en.wikipedia.org/wiki/Nickel-cadmium_battery.
2. *www.utc.edu/Research/CETE/electric.php.
3. *http://thefraserdomain.typepad.com/energy/2006/01/sodiumsulfur_na.html.
4. *http:/newenergyandfuel/com/2008/03/05/the-biggest-batteries-ever-answers-in-part-for-storing-wind-energy/.
5. *http://energystorage.org/tech/photo_vrb1.htm.