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Generally, is it better to let laptop and cellphone batteries fully die before recharging, to leave them plugged in constantly even when charged and not in use, or to unplug them once they are fully charged and leave unplugged until you notice the battery needs a reasonable amount of charging?

Now I know usage and specs differ greatly person to person, device to device. So I am just looking for some general feedback on the lifespan of a battery vs keeping it charged/letting it die.

I have struggled through the years deciding when to plug my phone and laptop in. I came to a decided perspective that it is better for the batteries lifespan to be plugged in all the time when not in use (not in use means I will use it later today or tomorrow and it will need juice). This maintains a full charge, while minimally using the battery thus increasing lifespan. Is this also optimal for minimizing power consumption? I have my doubts.

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Of course that depends on the battery, but Lithium Ion batteries were the standard for laptop/cellphone batteries last time I checked.

A battery feels most happy

  1. being neither too full nor too empty,
  2. being not too hot,
  3. being not charged/recharged too often.

If you don't need the battery, remove it from the battery pack (at about 60%) and store it dry and cool.

If you use the battery, make sure your laptop doesn't get too hot. Usually the processor is located near the "top" of the keyboard, away from your hands, but so is the battery.

There is power management software for many laptops, which ensures that your battery only gets charged once the charge falls under a certain threshold (e.g. 40%) and then charges up to 80%. This allows you to plug in/unplug your laptop (to move location) without initiating a new charge cycle, which would lower the life span of the battery.

(A friend of mine had a broken adapter, so the battery was charged/discharged every time someone bumped into the chord. After a few months, the 2-year old battery now lasts at most 2 minutes!)

For cellphones, it's inconvenient to keep them plugged into the wall all the time, so the general guideline is usually to charge it once it falls under, say, 30% and discharge it fully, followed after a full recharge, about once a month. The same holds true for laptop batteries, of course, but I usually find myself discharging them fully more than once a month anyway.

In particular, this means that the rule (myth?) "fully discharge before charging", which applied to old nickel-cadmium rechargeable batteries, does not apply to modern laptop/cellphone batteries.

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    This is very good info as far as extending the lifespan of the battery goes. But the second part of the question is in regards to reducing the amount of energy spent going through this charge discharge cycle. EG Should I aim to increase the lifespan of the battery or aim to spend as little time on the charger as possible? Or is there a middle path that addresses both? Where does sustainability meet on the issue of preserving the battery vs using as little energy as possible? – Enjabain Jan 24 '14 at 20:35
  • You can throttle your CPU, lower your display brightness and remove the battery and just run on the charger. I think this is the way to use as little energy as possible. The obvious energy saver is to turn off your laptop and just not use it whenever you can. That said, a laptop charger usually uses up to 60W, which before energy saving light bulbs would be the same energy a small bathroom light uses. If you really want to save energy, the laptop is not the place to start. Rather, fridge, hot water, stove, air conditioning, washing machine, etc. use way more in comparison. – Earthliŋ Jan 24 '14 at 21:27
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    Once the battery is unusable, there is also the issue of recycling the battery, so I think that increasing battery lifespan is always a step towards sustainability. – Earthliŋ Jan 24 '14 at 21:29
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    Some links would make this an excellent answer. – Móż Jan 24 '14 at 22:55
  • @Ӎσᶎ This is what I remember from reading several blog posts, computer magazines, laptop manufacturer's battery care advice, etc. I don't have a good link, but I'm sure that most pages linked on a web search of "battery care" or the like will give very similar advice. – Earthliŋ Jan 24 '14 at 23:09
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I read somewhere that one issue (of several) that tends to shorten the lifetime of laptop batteries is heat from other components inside the laptop. So, if you happen to not be "on the move" with your laptop all the time, but instead end up using your laptop at the same desk for several days/weeks in a row, then you should remove the battery (don't forget to turn off your laptop before you do that), and run your laptop from the mains. Then, obviously, put back in the batter when you need to take your laptop on a trip. I did that with one laptop and it seemed to prolong the life of its battery.

My most recent laptop has a battery-lifetime-extending mode in the BIOS, which, if enabled, prevents the battery from recharging more than 80%. The instruction manual claims that it is the final 20% charging of the battery that causes the most damage to the battery.

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