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Old January 21st, 2011, 07:24 AM   #1 (permalink)
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Default Food for thought about batteries and charging

In my wanderings about the forum for the last many months I've seen complaints about battery life, and answers about problems with batteries. Some of this has meshed in my head and I believe I can explain some of the seemingly 'bad' behavior we see reported (which happens at the end of this very long post).

To begin with, below are some points that *I* accept as fact about batteries and charging, and why I accept them.

1) The charger turns off so the battery won't over charge.
Yeah, we've all seen this. You plug in the phone before you go to bed, in the morning you unplug the phone, but you KNOW it didn't take all night to charge. Somewhere along the way the charger turned off.
Now there is some debate on exactly where the brains of this operation live. Some folks say it's the charger, some folks say it's the phone, some folks say it's the battery itself. *I* am of the opinion that it's the battery itself, and here's why. I DON'T believe it's the charger, I can't believe that $3 Ebay chargers contain that many smarts, but yet they work properly (usually). That puts it in either the phone or the battery. Now let's go to EBay and buy one of those cheap (excuse me, inexpensive) charger/battery combos. You know, the kind where you can plug the battery directly into the charger. Now I still don't believe the charger has 'smarts', but yet the battery doesn't overcharge, to ME that indicates that the battery controls the on/off state of charge for the simple fact that the phone has been taken out of the loop completely.
However, because we're all accustomed to seeing 'the charger is off' type terminology I'll use it here, but I don't really believe that's what's happening.

2) The charge light turns green before the battery is 100% charged
I've seen several reports of this. There is debate on when exactly the light goes green, some say 90% some say 95% - there is general agreement on somewhere in the 90's, for our purposes we'll use 95% as the threshold.
I believe this is true because of the battery charge cycles. Battery life is measured in charge/discharge cycles rather than age (of course age has an effect too). Batteries are good for X number of cycles, after that they start to degrade. For the sake of ease we're told that the useful life of a battery is about a year, but what we're really being told is it takes about a year to go through the number of charge/discharge cycles that will start to wear out a battery. I believe the light goes green to indicate 'cycle complete OK to remove charger' rather than '100% charged'. I think what the engineers are trying to tell us is that the battery is sufficiently charged that removing it from the charger won't 'waste' a cycle.

3) The phone always draws power from the battery, even when plugged in. This is actually a big one and kind of the thing that holds everything else together. We've all seen the threads about how "my battery gets really hot when plugged in and navigating at the same time". To me that indicates the battery is doing double duty - it's being both charged and discharged at the same time. If the battery were being bypassed and the phone drawing it's power directly from the charger then the battery would actually be cool.
And another simpler test, remove the battery from your phone, plug in the charger and see if the phone will turn on (it won't - or at least mine doesn't).
The reason the phone always pulls from the battery is so that it receives a constant amount of 'juice', which the electronics really like. Imagine the havoc inside the phone if it bypassed the battery to pull directly from the charger. You're at home and the phone plugged in, then somebody turns on the entertainment center with it's 200 inch big screen TV, 15 speaker surround sound system, blueray, dvd and vcr (for old times sake) players - the lights dim in the house. The phone would NOT like that (and we haven't even touched on the inconsistent current that goes to a power adapter in a car), to prevent a problem the phone draws power from the battery - only and always.

4) When plugged in, after fully charging the charger will not turn back on until the battery has discharged to a set threshold.
Another biggie. We already know that the phone always pulls from the battery (have you tried turning on your phone while plugged in but without a battery yet?). And we know that batteries have finite number of cycles until they start to degrade. For these reasons I believe that the charger won't turn back on until the battery reaches a certain level of discharge - in an effort to limit the number of charge cycles the battery goes through.
I've seen numbers from 75% to 85% as being the point at which the charger turns back on - for purposes of discussion I'm going to use 85% as the threshold (though I'd have no problem believing it's actually lower).
Because I've never seen the light go BACK to orange while on the charger, I also believe the light stays green as long as the charger is plugged in - rather than switching back to orange at 85% charge when the charger comes back on.

Now we get to real world examples.
Yesterday I was messing with my phone a lot and because of that I had to swap batteries late in the day. Therefore when I plugged it in last night it was showing 80% charge. This morning when unplugged it only showed 95% charge. Some folks would say that the battery didn't charge overnight and that there's a problem. *I* say that the battery was fully charged early - lets say at midnight - the charger shut off and that the phone ran on battery power all the rest of the night. So from midnight until 6:30 when I unplugged it, 5% of the battery was used. Because it didn't get below the 85% threshold the charger never came back on to bring it back up to 100%.


And more extreme, we've all seen the "My battery/this phone is crap - it used 20% in 30 minutes" threads (but then it turns out the remaining 80% lasts a reasonable amount of time).
*I* think that what really happens is that the phone was charged early in the evening and ran all night on battery. Meanwhile this person has 500 friends on Facebook who are all writing on the wall and sending Farmtown messages, also they follow 45 people on Twitter and pull email every 15 minutes and update weather every half hour and pull news headlines and and and...
In the morning when they unplugged the phone was at (for example) 87% charge. They fire up Pandora for 45 minutes and check the weather, thereby using 7% of charge. Suddenly the phone is at 80% charge but they've done 'nothing'. In reality the phone has been off charge and working fairly hard for 6 or 7 hours.

I also suspect (suspicion only) that it sometimes takes a few minutes for the battery meter to drop down to (the example of) 87% when first unplugged. I see this in reverse in my car. My car has a digital dash with little 'blips' for a fuel gauge - when I fill it with gas it takes a good minute or so for the fuel gauge to work it's way up a blip a a time to 'full'. It wouldn't surprise me if the battery gauge on our phones works the same way - once unplugged it takes it a few minutes to display the actual battery charge, working it's way down from 'full'. So if the person did glance at his meter right when he unplugged the phone it may still show 100% - or something close.

There you go then, that's my take on it all.
If you read this whole thing, kudos to you!

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Old January 21st, 2011, 09:21 AM   #2 (permalink)
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When I used to make Lasers, I would have to look at a lot of battery details, and IIRC, you're right about certain rechargable batteries ( I assume all cell phone batteries) having a circuit that prevents over-charging.
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Old February 3rd, 2011, 07:03 AM   #3 (permalink)
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As far as issue #1 goes.

If the charger output is 5V let's say, and when you start charging the battery it is at 4V. Depending on how low the battery voltage is, it will use more amps until it starts getting charged. The closer the battery gets to 5V the less amps it uses. So essentially it charges quickly at first, and then slows down as it gets close to being fully charged.

But when the voltage of the battery matches the voltage output of the charger, the battery stops pulling amps, i.e. it quits charging automatically. There is no need for any electronic brains to tell it to do this. It's just the nature of batteries and how they charge.
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Old February 3rd, 2011, 10:33 AM   #4 (permalink)
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Quote:
Originally Posted by offanairplane View Post
There is no need for any electronic brains to tell it to do this. It's just the nature of batteries and how they charge.
But they indeed DO have such circuits. One of the reasons that the battery has a temperature monitor built-in is so the battery can be optimally charged - for both reasons of safety and so that the user gets a decent number of charge/discharge cycles out of them (long-term battery life).

They're not your father's NiCads any more!

e.g., see this.
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Old February 3rd, 2011, 11:33 AM   #5 (permalink)
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Quote:
Originally Posted by erisuser1 View Post
But they indeed DO have such circuits. One of the reasons that the battery has a temperature monitor built-in is so the battery can be optimally charged - for both reasons of safety and so that the user gets a decent number of charge/discharge cycles out of them (long-term battery life).

They're not your father's NiCads any more!

e.g., see this.

Then what is the point in letting it run down to a predetermined level before kicking back on the charger, and running it back up to 100%?

Why not just keep a trickle charge going constantly so at any time when you unplug your phone it always has 100%?
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Old December 3rd, 2011, 01:42 PM   #6 (permalink)
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So I have a question. As an advanced user who really IS thinking a lot about the effective usage of various technologies and devices, I would appreciate some authoritative recommendation and/or explanation about the principle of the batterys.

What is the goal: I want to use my tablet in the way that in the office I put it into the AC supply not using the battery, using the tablet a lot as a "little computer" - for example a 2 hour skype-call. After that I need to leave the office going somewhere, where I connect to local wifi to check three e-mails, returning back to home, putting it to the AC supply and 1 hour using wifi and web.

I want to save the battery charging cycles, lifespan and things like that. I have thought that the device IS ABLE to run only from the AC supply. Why not? A desktop PC runs only from the AC power supply. A digital guitar multieffect the same (theese things often offer a choice to run from battery or AC supply). If some neighbour turns on his entertainment center, it should be catched out by the electricity installation and also by the AC power supply - in the case of the tablet or notebook - by the charger. If it is the cheap one $4 from eBay, OK, it is shit... But if it is the original one from Samsung, it should be able to protect the phone/tablet form some voltage shocks from the electricity...

I think it would be ideal for me, if the tablet asked me every time I put it into the AC supply, if I would want to charge or supply only with battery bypassed (disconnected) to save the cycles. I have seen this feature within some devices like a discman or something. So why not within the tablet/android phone?

Is this possible or it is absolutely stupid idea? If it is a non-sense, please advise me some other way of using the charger to save the lifespan and cycles.

Thanks a lot.
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Old December 3rd, 2011, 02:48 PM   #7 (permalink)
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Quote:
Originally Posted by Van Horn View Post
Is this possible or it is absolutely stupid idea? If it is a non-sense, please advise me some other way of using the charger to save the lifespan and cycles.
I don't think that it's nonsense at all - however, tablets are designed to be portable, non-tethered devices. That's the way that most people want to use them.

The best way to manage battery life is to keep it as charged as possible, actually. When batteries nearly reach full charge, the charging cycles reduce the current to the battery, giving it a trickle of charge. If you can manage to plug it in whenever you can while using it, I think it will last longer than constantly draining and charging. However, the batteries in modern portable devices include smart circuitry that try to manage the charge delivered to the battery. Because these devices try to judge remaining battery life based on drains and charges as you use the device, it is generally recommended that once a month or so you run the device to the point where it warns you it will shut down and then give it a full charge, to help calibrate that circuitry.

But, if you are able to plug in while using your tablet most of the time, without making it difficult to use, it is my understanding that this is the best way to maximize battery life for the device.
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Old December 3rd, 2011, 03:15 PM   #8 (permalink)
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Thanks for advice.
Yes, I am able to use it mostly plugged in. For ex. that skype call - you put on the headset having the tablet put on the table...

That is also the way I use my notebook - plugged in while I'm working and after that I for example close my notebook, bringing it somewhere else and continue... So this is the main task of the battery in my notebook - to keep it hibernated until I arrive for ex. from the office to home...

I bought a tablet to not to have to take the notebook with me every time - it's good enough to read and answer some mails and manage things.

When I had a Ni-MH battery in my cell phone, I was told not to charge it until it was "sufficiently drained", because of the memory effect of the battery. So you think I should this Li-something (probably Li-on) battery keep as charged as possible and drain it once a month, don't you?

Thanks.
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Old December 3rd, 2011, 03:22 PM   #9 (permalink)
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Quote:
Originally Posted by Van Horn View Post
When I had a Ni-MH battery in my cell phone, I was told not to charge it until it was "sufficiently drained", because of the memory effect of the battery. So you think I should this Li-something (probably Li-on) battery keep as charged as possible and drain it once a month, don't you?
Li-ion or Lithium polymer, yes.

That's what experts recommend.

This, I think, is the best site that I have found for battery information: Basic to Advanced Battery Information from Battery University

And this is a great page explaining how to best manage Lithium-based batteries, which power your phone and your tablet: How to Prolong Lithium-based Batteries - Battery University

(Note, however, in that page about Lithium batteries, that when he is talking about how best to store batteries, he is talking about what's best for batteries that not being used actively - in other words, if you swap battery packs to try to prolong life in an Android phone, it's best to charge the battery to 40% before you remove it for long-term storage.)
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Old September 4th, 2012, 07:55 AM   #10 (permalink)
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Some reaction to the "entertainment center" response:

I have found out, that many notebooks can be supplied only by AC adapter without battery, even if the mad neighbour is playing with his large entertainment center. The home circuit has to be able to solve problems with peaks... So I wonder why the notebook can run without battery and the tablet or phone cannot.... ? Thanks
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Old September 4th, 2012, 04:08 PM   #11 (permalink)
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Quote:
Originally Posted by Van Horn View Post
Some reaction to the "entertainment center" response:

I have found out, that many notebooks can be supplied only by AC adapter without battery, even if the mad neighbour is playing with his large entertainment center. The home circuit has to be able to solve problems with peaks... So I wonder why the notebook can run without battery and the tablet or phone cannot.... ? Thanks
Probably depends on the design of the specific phone/tablet/laptop in question. It's not like there is some kind of industry standard requiring or disallowing the behavior you describe.

In the case of the Eris (this is the Eris forum, right?), it is designed to be charged from a USB device - either a fake one like the A/C wall charger, or a real USB device (computer/laptop/hub). The USB spec only requires hardware designers to supply 500 mA at 5V ( == 2.5 Watts). And that means that if you start plugging the Eris into random USB equipment, you will certainly find one that is not capable of anything more than 500 mA.

It turns out that if you use the Eris on a voice call while otherwise fooling with it (say running an app that prevents sleep, or pulling down big files with WiFi), the battery will actually discharge even though you have it plugged into a USB device. That's compelling evidence that the Eris is designed to burn up more than 2.5 W of power in some "normal" usage scenarios. Clearly in this circumstance, the "extra juice" is coming from the battery - the USB port does not supply enough power to operate the phone correctly. (The cell radio RF power amplifier chip is rated at 2 Watts just by itself).

Note that this discharge (with the phone in use) doesn't happen with the Eris A/C adapter - it is rated for 1 Amp @ 5V, or 5 Watts - it is not a USB device; it just happens to use a USB cable.

So, as an example, there you go - the Eris was designed to make it possible to charge it from a computer USB device - and yet it can not be safely operated with just a USB connection because there is simply not enough juice for it.

That is a design decision; if you want to know "why", you need to talk to the individual handset, tablet, or laptop designer.


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