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Old 07-10-2014, 10:46 AM   #41
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The system has worked well, in that the battery rarely sits at 100% being charged, and only occasionally tells me that the charge level is getting too low.

Here's the battery usage report for the last three days:

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Old 07-10-2014, 04:58 PM   #42
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Originally Posted by TromboneAl View Post
The system has worked well, in that the battery rarely sits at 100% being charged, and only occasionally tells me that the charge level is getting too low.

Here's the battery usage report for the last three days:

Interesting, but the question still stands:

Is 'rarely being at 100% charge' better or worse than the extra charge cycles you are applying? Looks like you are averaging over one full charge cycle per day.


When I had DD's battery replaced under AppleCare, I think the warranty limits that Apple set was less than 300 charge cycles, and less than 80% capacity (three year warranty). So in just one year, you would exceed the point where Apple would do a 3 year warranty replacement.

Are you going from the frying pan to the fire?


-ERD50
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Old 07-10-2014, 07:15 PM   #43
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Is 'rarely being at 100% charge' better or worse than the extra charge cycles you are applying? Looks like you are averaging over one full charge cycle per day.
Nope.

Cycling is a big factor in reducing the capacity of LiIon and LiPoly batteries.


Depth of discharge also has an effect. Deeper discharges have a greater effect than shallow discharges for any given cycle count (a cycle is the amp-hours charged and discharged equivalent to a full discharge and recharge.)

Higher storage temperatures also shorten battery life. That includes sitting in a hot laptop running on the external power supply.

http://batteryuniversity.com/learn/a...ased_batteries

Quote:
Let’s look at real-life situations and examine what stresses lithium-ion batteries encounter. Most packs last three to five years. Environmental conditions, and not cycling alone, are a key ingredient to longevity, and the worst situation is keeping a fully charged battery at elevated temperatures. This is the case when running a laptop off the power grid. Under these conditions, a battery will typically last for about two years, whether cycled or not. The pack does not die suddenly but will give lower runtimes with aging.
I think that's Al's concern. The gotcha here is that the battery is still inside the laptop, still subject to high temperatures while the laptop is running.

Quote:
Another way to extend battery life is to remove the pack from the laptop when running off the power grid. The Consumer Product Safety Commissionadvises to do this out of concern for overheating and causing a fire. Removing the battery has the disadvantage of losing unsaved work if a power failure occurs.
So, there's that.

Quote:
“Should I disconnect my laptop from the power grid when not in use?” many ask. Under normal circumstances this should not be necessary because once the lithium-ion battery is full the charger discontinues charge and only engages when the battery voltage drops. Most users do not remove the AC power and I like to believe that this practice is safe.


Everyone wants to keep the battery as long as possible, but a battery must often operate in environments that are not conducive to optimal service life. Furthermore, the life of a battery may be cut short by an unexpected failure, and in this respect the battery shares human volatility.
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Old 07-10-2014, 07:55 PM   #44
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Man, to me all this trouble to "longify" extend the life of the laptop battery is too way much work.

I'd rather learn to day trade or something more fun like that. No, I would spend money for a new battery.
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Old 07-10-2014, 09:10 PM   #45
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Man, to me all this trouble to "longify" extend the life of the laptop battery is too way much work.

I'd rather learn to day trade or something more fun like that. No, I would spend money for a new battery.
When thinking about pct of charge we have to remember that what is reported is only a guess based on coulomb (electric charge) counting. It is not like an alkaline battery where the voltage is a good measure of remaining capacity. The battery management system firmware keeps track of all the charging - discharging to estimate the percent of charge. Of course this assumes that the total capacity is known and that the measurement is accurate. However the total capacity changes with various factors including age, and eventually the count does drift.

The only way to get to the physics of what is really happening is full charge/discharge cycles, in and of itself somewhat difficult on the battery.
The Li-Ion cobalt batteries are very flat at the nominal 100% of 4.2 volts. Only at the very extreme top above 4.2 does the voltage begin to spike up, and at the bottom, droop. Then the count (and possibly capacity) can be reset. When I worked on a BMS the state of health of the battery was a real issue, and lots of papers written on how to measure it. We never did figure out a good way to do it other than cycling to the extremes which we actually never did.

I think the problem we have with laptop battery life is that the way we need to use it eventually degrades the battery. It gets hot, and we discharge too much at the coffee shop, and keep it charged up when not in use partly to protect during a power failure. I often travel to hot places where I bring my laptop and charging when hot is hard on the battery. I agree with NW-Bound, I just figure I got to replace the damn battery every couple of years otherwise it is just too much of a headache.
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Old 07-10-2014, 09:18 PM   #46
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Quote:
Let’s look at real-life situations and examine what stresses lithium-ion batteries encounter. Most packs last three to five years. Environmental conditions, and not cycling alone, are a key ingredient to longevity, and the worst situation is keeping a fully charged battery at elevated temperatures. This is the case when running a laptop off the power grid. Under these conditions, a battery will typically last for about two years, whether cycled or not. The pack does not die suddenly but will give lower runtimes with aging.
I think that's Al's concern. The gotcha here is that the battery is still inside the laptop, still subject to high temperatures while the laptop is running.


So, there's that.
Yes, but it is still tough for me to understand just how much of an effect one is versus the other (enough to take any action?).

You (and the quote) mention 'fully charged battery at elevated temperatures' - OK, sample of one right now, but I've been on my laptop for hours now, and checking ambient surfaces around my desktop with the IR detector, I'm getting 74-75F, and the case of the battery is 75.5F max. I get ~ 84F around the left of the keyboard, so the batteries seem to be far enough away from that heat source. My little ASUS netbook, my older E-Machines laptop, and this Lenovo laptop all have the battery in the back, near the screen hinge, and that seems to be away from the heat.


Hmmm, doesn't charge/discharge elevate the battery temperature? Another possible negative side effect from Al's approach? [edit/add:] - well, FWIW, after discharge/charging from 85% back to 99%, the battery case is reading ~ 77F, so a bit warmer (and I imagine the cells themselves would be the source of the heat, so more change there). Significant or not, I do not know.

I like the approach of the FW control to stop charging at XX%. Then you don't have the added charge/discharge cycles. I'm not convinced T-Al's approach isn't doing more harm than good.

-ERD50
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Old 07-10-2014, 09:22 PM   #47
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When thinking about pct of charge we have to remember that what is reported is only a guess based on coulomb (electric charge) counting...
RV'ers who are seriously into boondocking with PV panels have a battery monitor that does that. Basically, it's just a digital voltmeter and ammeter interfaced to a microcontroller to do the "coulomb counting". They also compensate for the Peukert effect, which is pronounced for lead-acid batteries, but you have to take a guess at that factor to enter in. And yes, they can correct the initial battery capacity that you first take a guess at, but that requires running down the battery. Lead-acid batteries do have a more definite SOC (state of charge) voltage curve, but that is temperature dependent, so that requires a temperature sensor at the batteries.

There are several brands available, and they all want about $200. I have meant to build my own for my RV for a long time, just to get to do some soldering and write some firmware too. But I have been getting too lazy. I may still do that though, just to keep busy on something.
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Old 07-11-2014, 04:57 PM   #48
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In the "old days", if your device was plugged-in then you were charging your battery (no such thing as a 'smart charger'). Nowadays, when the smart charger in the device realizes the battery is fully charged, there is no charging happening...software turns it off. So because of that, and because lithium ion batteries don't have the memory effect of ni-cad batteries, I just let the device's software handle turning off the charger at 100%. I didn't research it, I just took the word of someone who did:
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Old 07-11-2014, 05:23 PM   #49
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Yes, but it is still tough for me to understand just how much of an effect one is versus the other (enough to take any action?).
I agree. Perhaps when you have a hammer (programmable timer), everything looks like a nail.
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