1.http://www.tecategroup.com/ultracapacitors-supercapacitors/ultracapacitor-FAQ.php#What_is_end_of_life_and_failure_mode_for_an_ultracapacitor
2. http://batteryuniversity.com/learn/article/whats_the_best_battery
3. http://www.ioxus.com/english/media/blog/five-questions-ask-when-buying-hybrid/