1) "A Mathematical Model of a Sealed Nickel-Cadmium Battery", Deyuan Fan and Ralph E. White, Journal of the Electrochemical Society, 1991, pages 17-25.
2) Understanding Renewable Energy Systems, Quashning, Volker, Earthscan Publications Ltd, 2005
3) .http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge
Webliography:
1) www.batteryuniversity.com
2) http://en.wikipedia.org/wiki/Nickel_cadmium_battery
3) http://www.evdl.org/docs/nicad-principles.pdf