My battery is at 100%, should I leave it plugged in?

I’m often asked the question of whether or not to always keep your laptop plugged in or to unplug it when it’s at fully charged. There’s been a lot of debate in the industry as to what the correct answer is to this question, and a lot of the answers are fueled by outdated or incorrect information. It can be hard to keep up with the torrent of information that comes through the IT industry on a daily basis but in my experience the most accurate answer to this question is: it depends.

There are a lot of factors involved that prepare my response when I’m asked this question, which is why I’ve provided different answers to different people. It really depends on a wide variety of factors such as the type of battery in the system and environmental concerns, such as if the system is heating up and if the person is looking at saving on their electric bill (for the more frugal of people).

Nowadays, most laptops are equipped with Lithium-ion batteries which the biggest concern with, in this regard, is heat. If you constantly leave the laptop plugged in and the battery constantly seems a bit hot, over time this can lead to a loss in charge capacity and can degrade over time. My recommendation in these situations is to unplug the system when the battery is fully charged, then plug in back in once it gets down to about 30-40%. When I make this statement, this sometimes leads into the concern of the “memory effect”.

The “memory effect” refers to an issue with certain types of batteries in where the battery appears to “remember” a smaller capacity that what it should. This isn’t a big concern of Li-Ion batteries, although some studies show that it does exist, but is most commonly a property of NiCad (nickel-cadmium) and NiMH (nickel-metal hydride) batteries. This can be caused from over charging the battery, serviced batteries, high temperatures, operation in below-freezing temperatures, inadequate charging times and a defective charger.

If you’re curious on which type of battery you may have, it’s pretty simple to determine. If you have a newer laptop, and have never replaced the battery, you most likely have a Lithium-ion battery. You can verify which type of battery you have by pulling the battery from the system and looking at the information on the battery itself. You will most likely see Li-Ion or NiMH on the battery somewhere. You can also consult the manufacturer (or person you obtained the battery from) and they should be able to provide you with more information.

In closing, as for saving money on your electric bills, depending on the type of laptop and its power consumption, the effect on your electric bill will most likely be very minimal. I would think that a typical laptop that’s always on and always plugged shouldn’t use more than $5 to $10 a month on your bill, and honestly I feel like that may be a bit of a high estimation on my part. If you are able to determine how much your laptop effects your bill, and you feel it’s much higher than that amount, I would think this would indicate an issue with the laptop, the charger or maybe even the electrical system.

I hope this answered the questions you may have on this topic. If you feel like I’m not correct in this article or want to add your own bit of information, feel free to leave a comment below. If you want me to explain further, feel free to contact me and I’ll be happy to help!

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