✔ 最佳答案
No battery is perfect. A charged battery will gradually discharge if left on its own.
"Self-discharge" is a characteristic of batteries. It is thought to be due to internal chemical reaction within the electrolye of the battery.
2013-12-15 00:38:27 補充:
Reference:
http://www.batteryeducation.com/2012/10/battery-self-discharge-rates.html