Battery drain in switched off laptops

Question

Say, I charge a laptop fully while using it, then once it's 100% charged, I switch it off, and don't use it again, at all, for around a month.

Will all the battery automatically have discharged due to self-discharge, and thus when I have to power it back on after a month, I will first have to charge it again and then it will power on?

Or, say if the battery is in good health, then the self-discharge won't be significant enough to drain the full battery power, and hence even after a month, I will be able to power it back on without having to charge it first?

My emphasis is here on the timeframe, like is a whole month enough to let the battery self-discharge fully?

Answer 1

It varies from laptop model to model. I have an old 32-bit Acer that loses only a few percent charge per week, and a newer 64-bit model with bigger battery that loses ~10%/week, fully shut down. There are a number of factors involved

• Intel® Anti-Theft Technology may continually try to contact a server even when the laptop is shutdown.
• Cell equalization within the battery, intended to increase battery lifetime before replacement and to prevent fires, may drain a bit of power.
• A number of models have particular problems with power drain, even when shut down.
• Use of Wake on LAN or Wake on keyboard or mouse requires that the CPU is running, though in low power mode, to detect the events.

So the only answer to your question is to research your particular laptop model, or better, test it yourself: shut down fully and check the battery a week later.

Answer 2

Generally, this should be fine. The exact amount of self discharge depends on a huge number of factors, but as long as it's a good laptop battery, it usually shouldn't be empty after a month.

Expanding a bit more, self-discharge of healthy lithium-ion or lithium-polymer batteries (the two types in predominant use in laptops tends to be a reasonably slow process that is proportionate to the capacity of the battery. More specifically, it's pretty typical for most such batteries, independent of their size, to take multiple months to self-discharge if they're not connected to anything.

You can generally reduce the rate of self-discharge by:

• Completely disconnecting the battery. This doesn't strictly reduce discharge from the battery itself, but it eliminates most of the small amount of current drawn by a modern computer when it's powered off (something has to have power to check when the power button is hit).
• Storing the battery in a location that's not too hot or cold and has minimal temperature fluctuations. Based on personal experience with rechargeable batteries of this type, somewhere around 15-20 degrees Celsius (about 59-68 Fahrenheit) seems to be a good temperature, and the less it fluctuates in the short term the better.
• Making sure the battery is room temperature before using it again. Cold batteries can provide less energy than appropriately warm ones. Again, this doesn't really reduce self-discharge, but it does help ensure the system is usable when turning it on again for the first time.

Also, it's probably a good idea to go about reconditioning the battery when you use it again if it's been unused for this long. To do this, simply discharge it as far as you can (preferably until the computer just shuts off, you can do this easily (albeit not quickly) by booting into the firmware setup menu and leaving the system sitting there with the screen on until it shuts off by itself), recharging it all the way afterwards, and then repeating the process once or twice more. This isn't quite as important as it used to be, but it can help keep the battery in good condition.