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On my Lenovo laptop, running windows 7, I got a prompt saying that, the system has noticed I am mainly using adapter, therefore I should keep the battery half charged. It justifies by saying, trying to overcharge batter reduces life time.

Now, form what I understand, the battery and charger should have internal circuits to prevent attempted over charging in the first place. Then, why is there a software level prompt to set the option to "half charge" battery, if mostly running on adapters.

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up vote 4 down vote accepted

The reason it's that way is because that's the way LiIon batteries work. Other battery types are happiest when fully charged, but not LiIon. I'm sure the laptop manufacturers would prefer otherwise, but you can't beat physics.

If you use the laptop on mains power most of the time, you should use one of the settings (if available on your unit) to charge only to 50-80%. Should you anticipate needing to use the laptop on battery for an extended period you can (in advance) change the setting and fully charge the unit.

One note: On my Sony Vaio the system sometimes "forgets" this setting, especially if the unit has been left on battery too long and runs the battery "flat". So check the setting from time to time.

Another note: Don't think you can do better by removing the battery entirely. Most laptops depend on the battery to supply "peak" power even when running on the adapter, and thus the CPU will likely be "throttled" if you remove the battery.

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... the battery and charger should have internal circuits to prevent attempted over charging in the first place. Then, why is there a software level prompt to set the option to "half charge" battery, if mostly running on adapters.

It makes sense even though it's quite an unusual one. The system designer could have set the charger to charge to only half charged once the system has determined that the user mostly uses the power adapter. But then when the user finally take the laptop out on an unusual trip and have to rely on battery, he would have only half charge at most.

So as to avoid having only half charge at most at all times, the system designer add a prompt to let the user choose. Only the user would know how he/she is going to use the computer, and the prompt let the system collect what is on the user's mind.

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Personally, I feel like this can be answered by a little light reading.

Let's look at what we're supposed to do to be able to use our battery for a long time.

  1. Don't discharge fully ever!!
  2. Don't store the battery at high temperatures.

And, from what I can tell, that's all that it comes down to. Your battery won't overcharge, it has security mechanisms in place. But if you constantly charge it to 100%, the process generates heat and heat is very bad for the battery.

The fact that the battery is at full capacity is irrelevant. Charging to 100% will just, most likely, produce a disproportional amount of heat.

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Half charging you battery is designed to keep your battery at a good state. If charging fully, then the battery can potentially lose energy over time, like wear out on a flat tire.

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How does only charging to half potential prevent energy loss? – Oliver Salzburg Mar 6 '12 at 12:43 something like that I think. don't quote me on it though - im no scientist. – SUPER MARIO BROTHERS Mar 6 '12 at 12:47
@OliverSalzburg - A battery is a chemical reacton that loses it ability over time. Charging to 50% capactiy saves some performance on the other 50% of the battery until you need it. – Ramhound Mar 6 '12 at 12:47
@Ramhound I would have expected something like that to be the actual answer to this question :P – Oliver Salzburg Mar 6 '12 at 12:51
in the end I was right though. a flat tire really ISNT a laughing matter. – SUPER MARIO BROTHERS Mar 6 '12 at 12:53

I would say it would be very easy to cut the power to Laptop power either via internal mechanism or Software, but unfortunately it seems that no one bother applying such solution to laptop batteries.

If you have hooked the charging cord to a Loptop continuously, within one month you will end up with battery backup time to just around half hour. One also can't keep hooking and unplugging the cords when you are home/office and wanna use laptop on AC power. This is what, the laptop manufacturers have to improve on yet.

After my second battery of laptop was died in short period, I didn't even bothered purchasing new and run laptop on AC power, coz its always on desk.

Unlike mobile batteries, laptop batteries can be ruined very easily.

Also for better battery life don't ever discharge it more than 30% of full capacity, or just once in 30 times you can discharge it fully.

Hope all of above makes sense.

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I've had this laptop for about 3 years. It's plugged in about 95% of the time that it's working. (It is unplugged between home and work.) I'm sure the battery has lost some "oomph", but I don't think it's more than maybe 20%. (But, of course, this laptop has a feature similar to the Lenovo in that you can set it to not charge to full charge.) – Daniel R Hicks Mar 6 '12 at 22:15
@DanH: So to which level you restrict the charging: 50% or 80% etc. If after 3 years your battery it good, then this is quite a achievement. – K. Shahzad Mar 7 '12 at 13:16
I've got mine set at 80%. (But note that the Sony battery is no great shakes to begin with -- 90 minutes of operation on a good day, when brand new. I suspect that some manufacturers over-stress the batteries to achieve longer run times.) – Daniel R Hicks Mar 7 '12 at 13:30

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