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General discussion

does MBP use fully charged battery with charger plugged in ?

Feb 9, 2011 8:56PM PST

hi all -
i recently came to know that the new polymer batteries with the MBP 13in do not suffer from memory effect.
moreover, one can even leave them on charge for extended periods i.e. even after they are fully charged.
the internal battery is equipped with sensors which prevent it from overcharging which was such a bane of older (probably ones still being supplied with laptops!) batteries.
so what i would like to know is whether the battery is being charged in any way after its fully charged but the charger is still plugged in?
so if the battery is full does the laptop sort of run directly on the charger bypassing the fully charged battery till its power is needed?
thanks!

Discussion is locked

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I believe that is correct
Feb 9, 2011 9:00PM PST

When the laptop is plugged into the AC adapter, the brunt of the electrical power is supplied by the adapter with a charge being applied to the battery.
Once the battery is fully charged, the charging circuit reduces the charge to just a trickle.

As soon as the AC adapter is removed, the charging circuit brings that battery into use, instantly.


Other theories may follow


P

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There is a chip
Feb 9, 2011 10:36PM PST

There is a chip and small bit of circuitry built into every battery for Apple systems, and pretty much any other battery where you can measure charge levels. That's how the charge level is monitored/reported.

While I can't always say this is true for other manufacturers, I think most all of them follow something similar if not identical. With Apple systems, the battery will be charged to somewhere around 102% of capacity. It's normal for them to be slightly overcharged. Then, if the AC adapter is connected, the SMC shut off the charging circuit until the battery gets down to about 95% charge. Even if you're not using it, the battery will slowly lose a charge, but it will take several days before you hit 95% on a battery that hasn't been consumed.

At some point, usually around 300 charge cycles, the battery will start losing its ability to store power, and the amount of time you can run off the battery will start dropping dramatically very quickly. That's your cue to get a new battery or have someone remove it if you have a MBP with a single piece bottom cover and the battery is locked inside. Fail to do so, and eventually the battery will start to bulge and deform your case, possibly causing other damage as well. If THAT doesn't get you to take action, then the battery will ultimately explode. Most of the time this is a slow process of over a year, but sometimes batteries fail and swell very quickly.

Also, just FYI, memory effect on batteries only applies to Nickel Cadmium (Ni-Cad) batteries. Lithium Ion (Li-Ion) batteries, which have been used in laptops for about the last decade or so, have never suffered from memory effect. The problem is there's just a lot of really old stale info about batteries still floating around out there. Fortunately you only tend to find Ni-Cad batteries in things like power tools and cordless phones these days, and Li-Ion is supplanting them slowly but surely in power tools.

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A few corrections
Feb 11, 2011 10:22AM PST

I'm not sure all of this information is exactly correct. On Apple laptops, the batteries are charged to 100%. They don't fluctuate between 95 and 102%. The controller can maintain 100% very accurately.

Futher, the 300 charging cycles you quoted is an absolute bare minimum that Apple quotes. It's probably based on full charge to full depletion cycles. Most people should see much better performance. For example, my MacBook Pro has had 481 charge cycles (though hardly any were likely full charges), and shows a capacity of 2069 mAh (milli-amp hours). Clearly, it's not anywhere near death, nor is it's capacity dropping significantly.

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It is
Feb 11, 2011 12:11PM PST

It is. I've seen Apple's own battery testing program say that the charge level is about 102% many times.

And 300 charge cycles is all the more Apple will warrant a battery for. And yes, it is from full charge to depletion, which is how ALL Li-Ion batteries are measured, so it's kind of a meaningless distinction to make. I won't get into the details of how Li-Ion batteries work, you can google it if you're interested, but let's just say that the cycles listed by system profiler are complete discharge cycles.

Trust me, there was a whole section on batteries in the Apple certification training material I had to slog through. What I said is accurate, and you can see it yourself. Take any Apple laptop, and once you get the charge level up to 100%, it will not charge again until it gets down to around 95%. If you have it on AC power, this will likely take about a week. You'll see the charge indicator gradually slip down. Or you could just look it up in Apple's documentation.

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That's not what you said before
Feb 11, 2011 2:07PM PST

I don't plan on getting into any kind of argument over this, but what you said was, "Then, if the AC adapter is connected, the SMC shut off the charging circuit until the battery gets down to about 95% charge." I don't know how to read that other than even if I have my MBP plugged into the A/C adapter, the battery will still discharge down to 95% before the adapter charges it back up again. This is simply not correct. The A/C adapter keeps the battery at 100% charge as long as it's plugged in. Trust me on this: real life experience bears this out, not some documentation. I keep my MBP plugged in almost all the time and it doesn't drop below 100% unless it's unplugged.

What you said about it not recharging until it falls to 95% is true, that's to prevent needless charge cycles of the battery for small charges. However, the cycle count shown in system profiler is definitely NOT complete discharge cycles. I can absolutely guarantee it's not, as I very infrequently let my battery get down to even close to discharged. The system profiler definitely counts a charge cycle at some point below 90% but definitely before a full discharge.

Finally, the amount of charge cycles Apple warrants has nothing to do with how long the battery should last. The 300 cycle count is the minimum you are guaranteed to get. It's like a car warranty. Just because the warranty is for 3 years doesn't mean the whole thing is going to fall apart in 37 months. My MBP is living proof that the average person should reasonably expect far more than 300 charge cycles in their battery.

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No
Feb 11, 2011 9:35PM PST

No, you're not understanding what I'm saying.

The SMC will stop the battery from charging once it is full. The laws of physics then dictates that the charge will gradually dissipate. If it kept the battery at 100% perpetually, you would chew through your recharge cycles in a matter of a few months. What you are describing violates some very basic laws of physics, and assumes a far greater level of technology than we have today.

I'll decline to teach you basic high school physics and Lithium Ion Battery Tech 101. Everything in my first post is accurate, and will be born out should you decide to research the topic. If you do, just remember that Wikipedia and random forum postings are NOT reliable sources. Any idiot can post something on Wikipedia, same as on a forum.

Finally, yes, 300 cycles is all Apple will guarantee the battery for. I make sure to mention that because batteries are considered consumables, and have a separate warranty from the rest of the system. At 301 cycles, the battery is considered consumed even if it is still performing well. If you go to Apple complaining about your battery with 301+ cycles, they are then going to tell you it is consumed and shoo you out the door most likely. Part of what I do with my posts is help manage people's expectations. Keep them from getting unrealistic ideas from people like yourself. I've seen batteries that are still going strong after about 600 cycles, and I've seen batteries that die within the first 100 cycles. Like everything else, battery manufacturing is not a precise process, there is a margin of error. Some batteries may have the energizer bunny of charging filaments, while others may have some anemic and sickly charging filaments that will not be able to handle a normal level of current for very long. Just because YOU have a battery that has lasted well over 300 cycles does NOT mean that the next person's battery will. That is a false assumption based on the human mind expanding your experiences to fit those of everyone else in the absence of any other information. It's a very common practice, but it doesn't make it any more accurate. After all, it would be folly to say that you and I are on the same caliber as say an Olympic gold medalist in long distance running, would it not?

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I knew you were Mr. Right
Feb 12, 2011 12:50AM PST

I knew I was dealing with Mr. Right after your first post. It's too bad you would rather digress from the original question asked and argue some strange points. For someone who claims to be a physics aficionado (I'll show you the "A" in my college physics course if you show me yours), you've made some strange statements that defy the laws of physics. I'm not sure how a battery can physically hold 102% of it's capacity. It let that one go before in the interest on staying on point, but since you are now attempting to discredit my answer and lead the person asking the question to potentially misunderstand?

Perhaps you meant to say that Apple batteries are officially rated conservatively and have the ability to hold slightly more mAh than is stated. That would allow them to be charged to more than 100% of their officially-rated capacity. However, a one-gallon bucket can physically only hold one gallon. There are no known laws of physics that allow us humans to overcome that. Now, if that bucket is actually slightly larger, then, yes, it can hold more than one gallon. But then, what it said it could hold and what it could actually hold are two different things.

Next, you claim that my statement that the A/C adapter will maintain the battery at 100% is wrong, and that would lead to rapid degredation of the battery. Yet you claim that instead, it lets the battery naturally deplete to 95% before recharging. Somehow, I'm supposed to believe this wouldn't actually create the very condition you describe, only worse.

Apple's 300 charge cycle is based on a heavy-use cycle. That is, nearly complete discharge and recharge cycles. Most people do not use their laptops that way. Those who do may expect not significantly more charge cycles. On the other hand, I described how I use my battery, which is not extraordinary in any way. There's nothing special about my battery or how I use it. I didn't get the "Superman" of batteries. Every battery made for this laptop is nearly identical from a consumer perspective. The deviation in performance and quality is too small to make a significant difference in charge cycles. To believe that Apple would allow a manufacturing tolerance of a 50% deviation from mean performance is simply ignorant. Therefore, the difference in battery performance is largely based on how the consumer uses it. Ergo, Apple warrants for a worst-case scenario, not for 99% MCBF (mean charges before failure). Again, as I have stated how I use my battery, it's nothing special--it's simply average use. Anyone who uses it in a similar manner could expect similar results. This is not an Olympic battery vs. the common man.

Finally, lest the OP freak out that his battery is going to suddenly swell up and burst the moment he goes past 300 charge cycles, I would like to point out that issues with batteries overheating and catching fire were quite the news story--two years ago. However, even then, compared to the number of batteries in service, the number of incidents was very low. Lessons learned have since been resolved and newer batteries (from reputable manufacturers) are extremely unlikely to have this issue. Newer circuitry in the batteries prevents the overcharging condition that lead to the overheating, which led to the swelling, bursting, catching fire.

If you'd like to discuss this further, I suggest you start a new post. We're doing a disservice to the OP here. Hopefully, he can separate the wheat from the chaff in what's been said already.

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Simple
Feb 12, 2011 1:47AM PST

It's simple really, the battery is only rated to store X amount of power, but that doesn't mean it can't store more. You have X grams of electrolytic gel, and you know that 1 gram of this gel can hold an average of say 50mAh of power, then it's simple math to go from there. But of course sometimes it's a little more or a little less. We're not talking about something like a graduated cylinder which can only hold 100mL of whatever you choose to put in it before it overflows. You're trying to make this into a bigger issue than it is in an effort to save face, which is about as obvious as it is ineffective.

As for the battery discharging, you're actually correct, and this is why it is generally recommended that you don't use your laptop on AC power all the time. It will kill your battery much faster. Again, this is Li-Ion Batteries 101. As for why it's allowed to discharge like that is that it slows the process a bit compared to rapid minor recharges. This gets into how batteries work. The actual mechanics of how the power is transferred to and from the battery. I'd say you can read up on it yourself, but at this point, who are we kidding?

And apparently you're reading only selected parts of my posts, because I clearly stated that the swelling and exploding is a slow process that begins after the battery has been consumed. I said that the battery starts swelling if you don't replace a consumed battery, and that it will eventually damage the casing. It's really interesting when you see a MBAir battery start swelling BTW. The older MBAirs, not the new wedge shaped ones. Those have a different kind of battery. Should you then fail to act at that point, then eventually the battery will explode. I do believe I also said that this will likely take more than a year.

The exploding batteries of a few years ago were all made by Sony and due to a manufacturing defect. There have not been any fundamental changes in battery tech since then that in any way inhibits this sort of thing from happening. There is absolutely nothing about newer batteries that says a brand new, just out of the box, battery could not swell up and explode on its first use. The number of batteries that do this is small, but Apple and other companies would not offer warranties on the batteries if there were no chance of them failing. They'd make a big deal out of marketing the fact that the batteries absolutely will not fail, blah blah blah.

Simple fact is, like any other mass produced product, you'll get some of them that are just absolute garbage right from the start. Can't be helped, it's just a part of large scale production. Other times, you get a product that just seems to last forever. You could have two cars roll off the assembly line one after the other. One will be in the repair shop almost indefinitely, the other just needs the regular oil change and never has any problems at all. Happens ALL THE TIME. Doesn't matter what the product is, that's just the realities of mass production. And since they can't possibly test thousands, tens of thousands, or even millions of individual products, they use statistic sampling methods to do quality control most places. Every so many batches of a product are tested, and if more than some acceptable number are bad, they scrap the whole lot. But it could easily happen that just by sheer dumb luck, that one batch tested was the only good one produced, and a whole bunch of bad products go out. It gets worse in that these days, everyone in the supply chain pushes the quality control onto the person below them. So Apple has a contract with its various suppliers saying that they will only accept a certain percentage of bad products from them, and if that number is exceeded, then there are some kind of penalty clauses that kick in. So if a company makes resistors that they sell to Apple, then they have to make sure they meet those quality standards. So they then push the same kind of crap on their suppliers of raw materials. It has to be of a certain purity, etc. It's a corporate version of pass the buck.

Finally, before you go calling someone Mr. Right, you may wish to look at your own actions. You keep insisting that I am incorrect, yet I don't see any evidence that you have made any effort whatsoever towards researching the topic to ensure that you are indeed correct. You insist that you are right, and I am wrong, even though I seem to be the only one who can come up with any specifics. Before you insist that you're right and everyone else is wrong again, maybe you should really spend some quality time with Google trying to research the topic. If you can come up with some solid evidence that I am mistaken, I'm not so full of myself that I won't admit I was wrong. I highly doubt you'll find such info for any of the core precepts, maybe some of the tangential areas where I might play a little fast and loose with the facts because, well, they're tangentially related, and I don't feel like explaining things like why batteries do not hold a charge indefinitely.

So, if we don't see you back for a while, we can assume that you're either busy with your research or found out that you were the one who was wrong and weren't able to admit it.

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I have nothing further to say here.
Feb 12, 2011 4:07PM PST

Grow up. If you'd like to discuss this further, I suggest you start a new post. We're doing a disservice to the OP here. Hopefully, he can separate the wheat from the chaff in what's been said already.

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Jimmy Greystone is right
Jun 21, 2011 9:23AM PDT

First of thank you OP and responders for this thread. Its answered a question I had about charging.

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95%
Jun 21, 2011 11:39AM PDT

Yes, that is correct, that the computer will not begin to recharge the batteries until the charge level has been depleted to at least 95%. Both Jimmy and I agreed on that point.