Re: Does a laptop battery drain even when the laptop is off?
Ziggler Mark is on point. Indeed, a laptop battery does in fact drain even while the laptop is off. Not only that, but let's say you remove the battery and put it in storage for an extended period of time, like a month or two without charging it, the battery will become completely unusable.
Laptop battery also have a finite number of charge cycles. And a charge cycle doesn't mean a complete empty to full recharge. A charge cycle can be wasted by just going from 90% to 100%. You want to preserve those charge cycles to extend the life of your battery. What I always advise my customers to do is if you're going to leave the laptop plugged in (treat it as a desktop) is to remove the battery the majority of the time you use it on the charger. So for example, every Saturday, pop the battery in, let it charge to 100%, then take it out, put it on the shelf and wait till next week to charge it again. The reason is, while the laptop is plugged in, the battery is constantly discharging and recharging itself in the background, burning through your charge cycles.
But back on topic, I agree with those who have said you may want to test that battery. An overnight discharge of 65% while in sleep or standby mode is definitely abnormal. What is the make and model of the laptop if you don't mind me asking?