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Comment by hmage | Hacker News Reader

You do know that keeping your li-ion battery plugged 24/7 is best way to kill it, right?

Do a full battery cycle at least once a month and you won't prevent the catastrophe.

Source: http://batteryuniversity.com/learn/article/how_to_prolong_li...

Storing a battery at 40 degrees C at 100% charge will degrade it by 35% after a year. Drop that to 25 degrees C and it'll be degraded by only 20% after a year. If it was stored at 40% charge instead of 100% charge that drops to only 4% degradation after a year.

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Aren't lithium ion batteries micromanaged to within an inch of their lives by electronics within the computer and the battery? Doesn't whether your machine is plugged in or not have very little to do with what the charge current to the battery itself actually is? Plus, of course, there's no guarantee that when the battery meter reads 100% the battery is actually full --- mapping 100% in software to 80% on the battery seems like the easiest way to improve lifetime.

e.g. it's very obvious that Macbooks have multiple different charging regimes, and they use different ones depending on what the laptop's doing and the state of the battery.

They are managed, yes, to provide the greatest out-of-box specs that they can then use for advertisement. "No one" cares about long-term effects, especially if those effects will be beyond warranty periods anyways.

Why can't this problem be solved in software? OS knows that AC power is used 100%, right?

I believe a better question is: Why can't this problem be solved in hardware? So, it won't depend on the OS and if I shutdown my laptop and leave it on the charger it will still work.

My 3.5 year old Asus laptop has still similar battery life as it had when it was new. I always keep it on the charger when I can and sometimes I just shut it down and leave it on the charger overnight too (but this is rare). When I bought it, I have noticed that the battery was never above ~95%, but I have never studied how it works exactly (is it done by HW or by the driver). I have used it with Win7, Win8, Win8.1 and now Win10.

Thinkpads (used to, don't know about these days) ship with a utility that allowed to prolong the lifetime of the battery by limiting the amount it will be charged. The article mentions "tlp" software which apparently does similar thing. So yes, it can be solved in software.

My lawn mower's LI battery is connected 24/7 and still works after 10 years, using it every summer. My phone battery recently died after almost 3 years but my previous phone battery still works 5 years later, both 24/7 on charge unless in mobile use. I think/thought the prevailing advice was that car batteries like lead/acid should be cycled (actually I know this) and the same for NICAD and for LI it has always been best to charge 24/7. Sometimes batteries including LI go bad, it just happens.

Doing full battery cycle every month sounds like a very bad idea for lithium batteries. You generally want to avoid deep discharges as much as possible, this is even pointed out in the link you posted:

"The shorter the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses"

Keeping the battery constantly at stable 60-80% charge is far better than doing full discharges every month.

To a first approximation modern li-ion batteries don't really care if they drain 100->50 once or 100->90 five times: the wear on the battery is more or less equal. Exposing your batteries to extreme temperatures (below freezing, above 40C) or allowing them to self discharge below the safe low voltage limit has a far greater impact on overall longevity.

That is to say: a lithium ion battery under use in a personal electronic device, whether kept charged or cycled, will be pretty well had it after 2 to 3 years, or at least have you thinking "gee, this battery sure isn't what it once was." I don't think it's possible to avoid this.

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