✔ 最佳答案
Since output of ac adapter = 65 w (assume output current is at maximum of 3.25 A)
output from transformer = input to ac adapter = 65 w (assume the adapter is 100% efficiency)
Because the transformer is 70% efficient, hence power input to transformer by the Li battery = 65 x (100/70) w = 92.86 w
Current delivered by Li battery = 92.86/12 A = 7.738 A
Time to run down the battery = 1.3/7.738 h = 1.68 h
The actual time would be shorter than the calculated one, as the ac adapter msy not be 100% efficient.
Also, you need to be aware that the current delivered by the battery is quite large. This may exceed the current limit of the Li battery, causing the battery to become hot or even broken down.
2013-06-04 20:00:48 補充：
Your further questions:
Power = voltage x current
Since power delivered by the battery = 92.86 W, and voltage of battery = 12 v
current = power/voltage = 92.86/12 A
2013-06-04 20:05:45 補充：
Given capacity of battery = 1.3 A.h (ampere-hour)
But amphere-hour = current (in ampere) x time (in hours)
thus, 1.3 = 7.738 x time
time = 1.3/7.738 hours = 1.68 hours
