Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

My laptop has the same issue as most laptops do have , it does not hold on to its charge for the expected amount of time . Now I have seen blog post that suggest to 'completely' drain battery power out . Now it is one of possible solution for shortened battery power , and many a times I have used my laptop till it hibernated automatically . The situation did not improve and I am not willing to buy a new battery . Now , my question is , there is an option in Windows power option how much battery power to reserve , usually it is set to 5% after which the laptop is set in to hibernate . Is it a good idea to change that number to as low as 0% to see if the condition improve ?

share|improve this question
    
It's not a good idea to drain any sort of battery to 0%. You're more apt to kill it than cure it. The way to preserve laptop battery capacity is to not charge it over 60-80%. Some laptops have controls to allow you to set this, others do it automatically. –  Daniel R Hicks Jul 20 '12 at 3:00

2 Answers 2

up vote 1 down vote accepted

First it should be stated that the expected battery life is set rather optimistically with a fresh, new battery. Every battery starts to degrade immediately and there are several factors which cause it to degrade faster and hold progressively less charge.

Heat will cause the chemistry to break down resulting in less capacity. You're basically cooking the chemicals in the battery causing them to break down.

Overcharging and overdischarging will both cause breakdown. If you overcharge, it causes heat and it tries to push the chemical cycle to reverse, but there is a limit. Keep charging and you won't push the battery to have a higher capacity. That's why there's a debate whether keeping the battery in while on AC is good or not. Most laptops will have some circuitry to prevent overcharging, but who's to say that your laptop manufacturer didn't cheap out and not install a really high quality controller?

If you over-discharge, you push the chemical cycle from charged to discharged and it may go to a point where the chemicals can't go back. Push too far and you may push the chemistry over the edge so doing a 100% discharge is not recommended as a standard practice.

The other issue is simply time - the chemicals degrade as time goes on just like food eventually goes bad.

That said, what are you doing when you do this full charge/discharge until the laptop shuts off? Basically you are retraining the laptop to recognize how much less capacity the battery has so the meter is more accurate, you aren't really helping the situation - you're hurting the battery. The laptop starts a timer saying - the battery is full. Then it waits until the battery signals that it is about to quit. The laptop then calculates a new Full to Empty equation to use from that point onward.

The old NiCad battery packs had a memory problem which the full discharge cycle was supposed to fix. Remember - you are not using NiCad any longer - you are using Lithium which prefers small, short discharges, and not really deep long ones. Some lithium packs are limited - they can only take something like a 1000 cycles - then they die.

share|improve this answer
    
nice answer ; I always looked for answers like this ; instead of trying to be superstitious about battery firmware . –  motiur Jul 20 '12 at 4:14
    
+1 for mentioning NiCad. NiCad is indeed old tech, but stories which where once true linger, even when we moved onto new tech. –  Hennes Jul 20 '12 at 12:31

"Completely discharging": It is actually dangerous to charge a li-ion battery once it has been discharged below a certain point (they will overheat rapidly, with resulting possible fire, etc.). So all li-ion packs, and even some individual cells, have a built-in chip called an "electronic fuse". (If you see cells advertised "with chip," this is what they're talking about.) If you somehow manage to discharge the battery below that point, the "fuse" will open and your battery is a paperweight after that! But, not to worry: The "0% charge" on your laptop's charge scale is at least 5 percentage points above this point. The laptop's power controller simply will not let you discharge the battery any farther. You would have to connect a load to the battery directly to do it. So... it is safe to tell Windows to let you go to 0%, in the name of "exercising" the battery.

HOWEVER... I've tried this a couple of times with aging batteries and it's never done a thing for my battery runtime.

It is not clear that deep discharge to near the electronic fuse point (which is to say, the point where the laptop forces shutdown) is damaging to a Li-ion. I've done this to my laptop batteries a few times and have not noticed any issues.

Because of the "electronic fuse", if you store li-ions for a long time, check up on them every two months or so - keep them between 40 and 60% charge. They self-discharge very slowly, but if left for a long time they could self-discharge far enough that the "fuse" will open and you won't be able to charge them again.

Re overcharging: ALL laptops (in fact, all equipment with built-in Li-ion charging circuitry) stop charging when the battery is fully charged and are incapable of "overcharging". The circuitry for this is a single charge controller chip, ridiculously cheap. Manufacturers do not cheap out on this because they do not want their products associated with large numbers of battery fires, which is what would happen.

What does damage laptop batteries if they are left "on charge" too long is heat. This is mostly dependent on the laptop design - if the battery is where it will pick up heat from the hard drive or CPU, its runtime will be degraded sooner than otherwise. So in those systems it IS a good idea to not leave the battery in the laptop once it's charged. The laptops where a part of the battery hangs out beyond the laptop's normal perimeter are actually a good design in this regard!

"Recalibrating": Laptops do not use any sort of "timer" to determine battery remaining charge. (This would be useless as you can easily change your battery drain by a factor of at least 2:1 by varying the screen brightness, by using your hard drive a lot or a little, same for CPU, etc.) They use the battery terminal voltage.

My attitude is that life is too short to treat laptop batteries with kid gloves. I treat mine like I treat the gas tank in my car: I use what I need to use from it, whether that's a little or a lot, and when I can charge it I charge it completely, in case I'll need to use it a lot. I've never had cause to complain about the results.

A lot of the lore about li-ions, in particular the notion that they really don't like deep discharge ("recharge early and often"), seems to come from a web site called "Battery University". It is not a reliable source.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.