Notebooks and batteries

[Cheezdoodles]

So, my new laptop (acer aspire 3820TG) has quite awesome battery life (9 hours if i turn down lcd brightness and wifi).

I want it to stay like this for as long as possible (i realize it will get worse, as battery life gets worse with age).

Im wondering about the following:

Is having the battery plugged after its fully charged destroy battery life quicker than removing it?

Should i unplug my battery when its fully charged and i have power through the adapter(plugged into the wall).

AFAIK it has a trickle charge system, which means it will continously load the battery to maintain it at max.

I know that with my old laptop, it lost its battery life very quickly due to me having it plugged in to the power while fully charged all the time (and the laptop was usually in the power adapter the entire time!).

 

[dZeus]

So, my new laptop (acer aspire 3820TG) has quite awesome battery life (9 hours if i turn down lcd brightness and wifi).

I want it to stay like this for as long as possible (i realize it will get worse, as battery life gets worse with age).

Im wondering about the following:

Is having the battery plugged after its fully charged destroy battery life quicker than removing it?

Should i unplug my battery when its fully charged and i have power through the adapter(plugged into the wall).

AFAIK it has a trickle charge system, which means it will continously load the battery to maintain it at max.

I know that with my old laptop, it lost its battery life very quickly due to me having it plugged in to the power while fully charged all the time (and the laptop was usually in the power adapter the entire time!).

I know with my Thinkpad, the power manager recommends the following if you want to maximize lifetime:
- do not fully charge the battery but only to 90%
- and further more, only start charging when the battery level drops below 70%

I've heard that Apple notebooks work similarly (don't know about the exact levels though).

If you don't use the battery for an long time, I've heard that the best way to store it, is to cool it while it is charged at around 70% (and once every so many months recharge it to 70%). Of course, if you want to keep the battery refrigerated, you need to put it in a vacuum sealed bag with some anti-moist (silica gel?) inside the bag.

 

[Sxotty]

dZues' advice is good. It may not really matter much though. If they put in good batteries then they will probably last longer than your laptop.

One thing to keep in mind is that the cycling already done is important. With lithium batteries there is irreversible capacity loss right at the beginning of life. If they did not already cycle the cells b4 they made the battery then you will have a significant amount of degradation like as much as 10-15% of initial capacity. Most cells are "formed" before the get into your system though so a user will not notice that unless the manufacturer chose to skip it so they could claim higher initial capacities.

Personally I doubt that the percent matters that much, but if you can keep it between 35%-100%. The plug thing should be in the past if manufacturers would do a decent job. It should be relatively simple to quit charging. The should hold the battery at a certain voltage until the current decreases past a certain point and then completely quit charging.

 

[Grall]

Of course, if you want to keep the battery refrigerated, you need to put it in a vacuum sealed bag with some anti-moist (silica gel?) inside the bag.

It's not neccessary to bother with silica gel unless perhaps you live in a rainforest and your ambient air carries 100% moisture level when you put the battery in the bag. Just squeeze out any excess air before you twist the bag shut, then let the battery warm back up to room temp before using it again.

 

[Cheezdoodles]

So no point in removing the battery when its fully charged??

 

[Sxotty]

My laptop has an option that I set to stop charging at 95% of capacity. I set it to only charge when below 90%. You could so something like that and if the battery isn't self-discharging and you use it like a laptop then it will probably work out well for you (what I mean is if you unplug it and use it on battery power, if you never use battery power then take it out by all means). It is a fact that at lower temps and voltages there is less degradation. Laptop cells have a more sloped discharge voltage profile than some types of lithium batteries. This means that when you max out the charge the voltage increases significantly over a lower charge. At higher voltages there is more potential (pun eh ) for electrolyte breakdown. And if you remember Arrhenius' law then you know that temp has the same effect. Try to keep the battery at room temp and not quite maxed and it should last quite awhile.

I imagine the heat from the CPU/GPU and other junk in the laptop is harder on the battery than anything else. It probably results in uneven wear since some cells will be closer to the heat source and others farther away. In any case I imagine that is a much more important reason to remove the battery if worried about premature wear. So if you are doing computationally demanding stuff it might be worthwhile. Right now my laptop is running models which max out one thread for hours at a time. I don't bother to pull the battery b/c normally I use a desktop, but if I were to regularly do this sort of thing I would probably pull the battery.

http://www.candlepowerforums.com/vb/showthread.php?275159-Samsung-3000-mAh-18650-Testing
shows some discharge profiles. The tester cut off right near the bend. If you look at the left of the charts you can just see it though. If your battery is starting up that bend then you are charging it too far. Not much energy is available there though b/c the voltage ramps really fast (which is why over voltage protection isn't that difficult), but it is better to not start up that bend at all. I don't know what type of cells are in your battery pack. If you could figure it out you could make a very good decisions. Anything over 4V is heading into a place where you can have significant breakdown. I would say 3.6V or less will protect the cell from many side reactions that can diminish capacity. So if your cells have a lower potential to begin with they are safer in many ways though the energy density is also lower.

 

[green.pixel]

and further more, only start charging when the battery level drops below 70%

I've been reading that the best for battery's health is to start charging it when it drops to around 20%, so it can do complete cycle or something like that.

 

[Frank]

The single most important factor on battery life of Li-Ion batteries is heat, and the most important heat source is most of the time a blocked air opening (unless you have a fanless netbook or something, of course).

For example, if you like to watch a movie or browse in bed and you put the laptop on top of the sheets, it heats up quite a bit and degrades the battery more in a short time than any kind of charge setting can prevent.

Also, many times when people start complaining about the battery life, it turns out they have a mostly blocked fan due to dust (which looks like felt by that time).

And lastly, it can simply be needed to have Windows reset the empty/charged thresholds, as they change (slowly) over time.

Btw, all Li-Ion batteries have a microcontroller or other protection circuit build-in or attached when used (it can be in the battery pack or charger/device) that monitors the cell health, prevents overcharging (and thereby melting/exploding it) or draining it completely (and thereby shorting it), etc. They just degrade by charging them and over time (depending on heat).

So, you might improve battery life a bit more by never discharging it below 20% or charging it above 80%, but keep in mind that the protection circuitry already does something alike, although within smaller margins (something like between 5-10% and 90-95%, depending). And that is when the battery is empty/full.

 

[Kurt]

And lastly, it can simply be needed to have Windows reset the empty/charged thresholds, as they change (slowly) over time.

How would I go about that

 

[Zaphod]

Look in the manual. Some have an option in the BIOS to trigger it, others trigger it whenever the battery is fully depleted to the point where the protection kick in and shuts the battery off.

Most likely this won't give any more battery life (unless the values stored in the battery have gotten screwed up somehow), but it will make the time-remaining-gauge and whatnot accurate again to the current capabilities of the battery (i.e. it resets max capacity, discharge curve, etc.).

 

[Albuquerque]

How would I go about that

Depends on the hardware, both in your laptop and in your battery. Some devices do not allow this, others might support it at a hardware level but finding the software can be difficult.

The battery contains a small microchip that keeps track of when a battery is "empty" and when it is "full". It contains a small voltage look-up table that allows the chip to communicate level of charge to the upstream hardware (ie, your laptop's DC-to-DC converter) about the capacity remaining.

The only way you can really infer how full or empty a battery might be is to monitor the voltage plane, sometimes that lookup table will get skewed as the battery cells age. Some battery microchips allow you to basically recalibrate that lookup table by fully charging the battery, fully draining the battery, and then fully recharging it again to completely cover both ends of the empty/full spectrum.

Your laptop has to support this method too, as it basically means that it will run the battery to zero voltage while continuing to operate -- most laptops will forcibly turn off before the battery is truly drained.

 

[Kurt]

OK, I thought it was something that could easily be done from within Windows.

 

[Sxotty]

Depends on the hardware, both in your laptop and in your battery. Some devices do not allow this, others might support it at a hardware level but finding the software can be difficult.

The battery contains a small microchip that keeps track of when a battery is "empty" and when it is "full". It contains a small voltage look-up table that allows the chip to communicate level of charge to the upstream hardware (ie, your laptop's DC-to-DC converter) about the capacity remaining.

The only way you can really infer how full or empty a battery might be is to monitor the voltage plane, sometimes that lookup table will get skewed as the battery cells age. Some battery microchips allow you to basically recalibrate that lookup table by fully charging the battery, fully draining the battery, and then fully recharging it again to completely cover both ends of the empty/full spectrum.

Your laptop has to support this method too, as it basically means that it will run the battery to zero voltage while continuing to operate -- most laptops will forcibly turn off before the battery is truly drained.

It aint going to zero voltage no way. You would not have a battery anymore then. That really isn't how it works.

 

[Albuquerque]

It aint going to zero voltage no way. You would not have a battery anymore then. That really isn't how it works.

While 'zero' voltage may not be specifically right, draining the cell to within the lower boundary of any usefulness is a bit more abstract and hence I went with 'effectively zero' as it has no effective use below that point.

Nevertheless, is there anything else you'd care to expound upon other than simply saying "that isn't how it works"?

 

[Sxotty]

Well I would say that usually the loss you are accounting for is either irreversible lithium loss (it gets stuck between other atoms), or increased internal resistance. If you are losing lithium ions alone then you really don't have much of a problem in terms of predicting the percent of battery capacity. When you look at a discharge profile it keeps the same shape, just is shifted. So that means the voltage lookup table is still perfectly right. Instead you just need to literaly time the discharge so you can tell a user "your battery is 70% full and time remaining is X" where X is less than it originally was. If the battery is building up impedance due to growth then you would need to rewrite the voltage lookup table. Different batteries show different degradation mechanisms though. So what would be effective in terms of measuring and predicting battery capacity would be more or less complex depending on the makeup of the cell.

The zero voltage thing was just a comment about damaging the battery. There actually is useful energy below the cutoff that is used on many cells, just not repeatedly b/c you ruin the cell. It is also a way a company can say our cell has super duper specific energy capacity. We charge to an outlandish voltage where the cell breaksdown, then discharge to an absurd voltage as well. Look how big our number is for the first 10 cycles

 

[Frank]

The zero voltage thing was just a comment about damaging the battery. There actually is useful energy below the cutoff that is used on many cells, just not repeatedly b/c you ruin the cell.

If you look at it in that way, much (if not most) of the potential power is still in the cell when it drops off below the point (voltage) of being usable, it simply isn't able anymore to deliver the requested/specified wattage without getting destroyed.

If we would incorporate a DC/DC power regulator in the battery and increased the size quite a bit, we could get much more power out of it.

Unfortunately, that would increase the size and weight quite a bit (and make the electronics more expensive), so it isn't used. Because we want our battery-powered devices to be as small and light as possible, and the battery is already taking up more than 50% of that as it is.

A better alternative is Li-Po batteries, but they're much more challenging and thus expensive to produce, in smallish quantities.

Even more so: the idea behind Li-Po batteries is creating larger reactive surfaces. We can still go quite a way with that for creating better batteries.

Hard to figure out and translate into production machinery, but the idea is solid and the materials required quite cheap.

 

[Albuquerque]

Instead you just need to literaly time the discharge so you can tell a user "your battery is 70% full and time remaining is X" where X is less than it originally was.

This is exactly it, but that detail is not contained in the OS, it's contained in the logic chip of most modern laptop batteries. Hence having issues with a battery that's 90%, then 80%, then 15% suddenly... This curve isn't stored anywhere in the OS, it's on the chip in the battery (which is why reloading Windows doesn't change your battery wear indicator.)

So what would be effective in terms of measuring and predicting battery capacity would be more or less complex depending on the makeup of the cell.

Hence why it must be specifically supported by the vendor of both the battery AND the hardware using that battery. Which is also why, you hope, they will have the proper algorithm in their application for doing this work.

 

[eastmen]

Personaly if i'm at home on the couch and can plug my laptop in or in bed or what have you. I just take the battery oout and let it run off the ac power and only use the battery when i need too. At my old job I had a laptop and 2 batterys for it and both would barely hold a 30 minute charge (when new they held a 2h10m charge) when i was laid off. They were constantly used and charged .