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Should You Keep Your Laptop Plugged In or Not?

 

By Stanley Zarowin
Feburary 2008

SHOULD YOU KEEP YOUR LAPTOP PLUGGED IN OR NOT? 
My primary computer is a laptop. I keep it plugged in all the time so when I travel I just pull the cables and I’m off with a fully-charged battery. But I worry that by leaving it plugged in I may be shortening the battery’s life. I’ve asked tech-support people about that. Some say it’s definitely bad for the battery, and others say that’s hogwash. What’s the straight story?

 Before lithium-ion (Li-Ion) batteries replaced the old nickel-cadmiums (NiCad) and became the standard for laptops, it surely was unwise to leave the battery plugged in for long periods. That was because if a NiCad was not nearly fully drained periodically and then recharged, it would lose its ability to ever become fully charged; that was called the “memory effect.” Li-Ion batteries overcame that shortcoming, but the hazard common to both batteries is heat, which degrades their capacity. Not only do batteries generate their own heat when they’re in use or being charged, but the computers they power also radiate heat. Typical temperature levels in a battery-powered laptop reach 140 degrees Fahrenheit. Be aware, too, that the electronic components of an always-on computer also degrade somewhat from exposure to continuous heat—whether on battery or AC power.

The other issue is charge-cycle times. Li-Ion batteries have a typical life cycle of around 400 charges, so after about a year of typical use, it will degrade to about 80% of its original capacity. But if it’s plugged in all the time—thus continually being topped off—that adds to the number of recharge cycles and hours of continuous heat exposure.

So what can you do? Let’s address the heat problem first. You can’t eliminate the generation of heat, but you can do things to alleviate it. For example, if your laptop sits flat on your desk, cool air cannot circulate under it. But if you elevate the rear of the laptop so it’s tilted toward you, the warm air can escape. Do an Internet search for laptop cooling and you’ll see a wide assortment of devices—from simple stands that elevate the rear of the laptop to fan-powered grills that circulate air under the computer (see screenshot at left). These devices provide a bonus: Slightly elevating the rear of the laptop improves access to the keyboard.

So I would suggest this strategy: If your laptop is going to be plugged into AC power for long periods, remove the battery after it’s fully charged. Then, every month or two, install the battery and let it recharge because even when it’s not in use, its power slowly drains. When it’s full, remove it again.

To check a battery’s power level (if the power meter icon is not already in your taskbar—see screenshot), go to Control Panel , Power Options and access the meter. With that strategy you will always have a fully charged battery available for travel.

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