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It's true that keeping lithium batteries fully charged degrades them quicker than at half charge (PDF). I bring my laptop with me in the day, but run it on the charger in the evenings.

Besides removing the battery (not possible on many new laptops), is there a way to run the laptop off the AC adapter without the battery charging?

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Unfortunately, I don't think there's a general solution to this problem, although I'd be happy to be proven wrong.

Certain laptops do have the ability to cap the battery charge. For example, my Toshiba laptop (and presumably other Toshiba models) have a utility that implements an Eco Charge Mode. And apparently the Quickset utility on at least some Dell laptops can be used to disable battery charging, which would let you manually cap the charge. You might try to find out if your laptop has similar features.

That said, I don't think your particular use case should cause too much worry, since you don't keep the battery at full charge for extended periods (days, weeks, etc.). If you want to minimize the full-charge duration, consider putting your laptop to sleep (rather than hibernating or powering down completely) so that the battery discharges a little overnight.

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    ALL laptops, and everything else that uses Li-ion batteries for that matter, stop charging the battery when it's fully charged. There is no such thing as "overcharging". If they did, the battery would overheat and fail, and possibly catch fire. – Jamie Hanrahan Sep 25 '14 at 9:28
  • The term "overcharging" does not appear in my answer. We're talking about keeping the battery "fully charged", which most devices will do. This often implies some level of trickle charging, but no one is claiming that the batteries are being "overcharged". – jjlin Sep 25 '14 at 16:36
  • No, but the term does appear in many similar answers, so I include it on a cautionary basis. And you're flatly not supposed to trickle-charge a li-ion to keep it at 100%. You're supposed to STOP, as in 0 mA, charging once the battery is fully charged. If the terminal voltage drops far enough the laptop will start charging again, but not "trickle-charging". – Jamie Hanrahan Sep 25 '14 at 17:09
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    I suggest being a bit more discriminating in where you paste your comments then. As far as trickle charging, yes, that was poorly worded. More of a topping-off when the voltage drops again. – jjlin Sep 25 '14 at 18:38
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Some laptops permit operation with the battery removed from the battery bay. In addition to stopping charging, it prevents exposure to potentially damaging heat—heat is the main contributing factor to premature failure of laptop batteries. Both of my laptops (HP Pavilion dv6z-3000 and Clevo P157SM) can run without a battery attached. To test whether this can be done safely, turn off the computer, remove the battery with the AC adapter plugged in, and try turning it on. If it turns on, you should be OK.

Some laptops may not be as well-behaved when you do this, with reduced performance when the battery is removed especially if the AC adapter can't supply enough power for full-load operation (such as when gaming). While neither of my laptops do this, this is worth noting.

Be sure to put the battery back in before you unplug, though!

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