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I want to download torrents while keeping the device plugged to charge. My device is made by Samsung.

Is the power consumed from charger, or battery, to power the device when charging? Will my battery take a hit?

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Of course your device requires power to run – whether you've set it for charging or not. Question is: Does it use more power than it gets by charging? Which depends on multiple factors:

  • Your "power source". USB only charges with 500 mA (USB2) resp. 900 mA (USB3), A/C with up to 2 A.
  • Your devices power consumption. Depending on what it's doing. Display turned on max brightness already uses more than USB can provide, recording/playing HD videos takes bit bites, and even a WiFi download might exceed that (see the table in my answer here for some example values).

So in your case, all depends on the power source. If it's USB, it might just "hold the charge", get a "trickle" or lose "a trickle" or more when downloading on WiFi – or probably constanly lose charge when on mobile data.1

Btw: Your device might get quite hot in either case :)

Edit: Reading your question again after the discussion in the comments, it looks like I've missed a major part of it. Asking whether the "battery will take a hit", you most likely wanted to know if "torrenting while charging" causes any harm to your battery. Hard to say absolutely, as it depends on device an battery; but a good indicator is "temperature". Batteries used today are mostly Lithium Ion (LiIo), seconded by Lithium Polymer (LiPo). Both have in common not to like "extreme temperatures". So if in the process the device gets hot, that's an indicator your battery might not like that for long.

For details, please also see our tag-wiki and tag-wiki. Both give general information on them.


1: Note that the values in the linked post are exemplary only; your device might differ, but relations will be comparable.

  • Well, what if the device was powered off (although that's precluded by the question)?😉 – Tamoghna Chowdhury Nov 27 '15 at 8:28
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    @TamoghnaChowdhury Then you can't download torrents 😉 – Izzy Nov 27 '15 at 13:08
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    This doesn't really answer the question of "does it use battery or pass-through from the charger when the charger cable is plugged in". And the answer is, it depends on how that particular phone was designed. Although I presume most use a pass-through and then trickle charge the battery with whatever is left over - as you can pull the battery out of the phone and it will run just fine from the charger cable. – SnakeDoc Nov 27 '15 at 17:36
  • If consumption is higher than feed, the "battery will take a hit". And as you correctly stated, @SnakeDoc, whether power is "passed through" depends on design; I doubt a generic answer to that is possible, so I've skipped that part. Maybe I should have explicitly stated? – Izzy Nov 27 '15 at 17:41
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    @SnakeDoc There really isn't a concept of "pass-through" in most battery setups. Either current is moving "into" the battery in the mode in which it does work to result in increased chemical energy in the cell (net charge) or it's moving "out" of the cell (net discharge). It's not like a single battery cell has multiple cathode and anode connections, so it could be charging into one point and discharging out the either simultaneously. The only "round trip" power might make is down-regulation from 5V to battery charging voltage back up to voltage needed to run core/etc). – ζ-- Nov 27 '15 at 18:00
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Tests done to arrive at the answer posted below were correct but the interpretation of results was erroneous on my part. This was validated by two sources including Battery University and based on the correct interpretation and additional inputs a separate answer has been posted. This also helps in readability and understanding


Power is consumed by the phone from the battery when charging, if in use, as in your case.

Point to understand here is that two simultaneous processes are happening, of topping up and draining. If the battery charging algorithm and implementation in OS is not well designed and implemented, there's a possibility that this situation ends up "confusing" the charger process into thinking it is supplying less charging current when it is not.

Hence a safe practice is NOT to use the battery when it is being charged. While I cannot talk authoritatively about your phone battery being hit, better to stick to safe practices in interests of battery life

Quoting from Charging Li ion batteries, which gives a view of three stages of battery charging and current/ voltage behaviour in these stages (emphasis mine to highlight)

"Some portable devices sit in a charge cradle in the on position. The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because it induces mini-cycles, but this cannot always be avoided...."

"A portable device should be turned off during charge. This allows the battery to reach the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low by drawing a leakage current. A battery may be fully charged, but the prevailing conditions will prompt a continued charge, causing stress."

Link posted from "Battery University", has many other informative articles on battery charging which may help

EDIT

Want to add diagram from Battery University link above and explain the impact of "parasitic load":

Three stages of charging
Three stages of charging (click image to enlarge)

In this typical example, charging completely is shown to take little over 3 hours with "saturation stage", accounting for 2 hours.

In the saturation stage, the voltage add to the battery is not increasing and the current is steadily decreasing.

Now, when you are downloading a torrent , assuming through WiFi, it takes 550 mW (for Samsung Galaxy S3), which is heavy duty. Thanks to @izzy for pointing out the source in his answer here.

This load will definitely divert a part of current towards torrent download (am trying to determine how much ). Whatever be the exact value of that current, it will continue as long as downloading happens and the tapering of current as shown will not happen. This is the first detrimental effect

Next, because of this current, the voltage, instead of being flat, will increase and more threatening aspect is towards the end of saturation stage. Here, the voltage is expected to fall sharply once the maximum voltage is reached, but will not happen since the parasitic load (torrent load) current is not tapering. This would result in battery staying at maximum voltage, which increases the temperature internally and creates stress in battery, damaging it.

A related aspect is that cell phones are designed to discharge rapidly from 100 to say 90%, which may be noticed say compared drop time between 80 to 70%, with same usage. This is designed so that cell temperatures internally are kept at maximum for least time. More on this Your battery guage may be lying...not a bad thing

EDIT 2

I carried out tests using Honor 6 , and results to my mind conclusively point to saying don't use the battery while charging.

These test results are on the sister SE electrical site and am hoping to get their view on that as well. Would update here once I get more inputs

Till then,

Don't use the phone while charging, at least for downloading or uploading or any other heavy duty (high power consuming activity).

This appears to be better approach, since using the phone while charging can't be avoided

While I suspect device manufacturers would have catered for minimal loads or usage while on charge- I haven't been able to investigate this as it is not documented AFAIK.

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    Modern batteries wont have noticeable impact on battery life even while usage during recharge. And there's basically no real battery harm in doing so either. I have been personally doing this since years! Modern batteries and algorithms to deal with them are pretty smart. – Jaskaranbir Singh Nov 27 '15 at 2:50
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    Since the charging circuit is built into the device, you'd hope it would be designed to charge while the device is on. – immibis Nov 27 '15 at 9:17
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    I have a battery pulled out of a Droid RAZR HD which will testify to the truth of this post. It was overcharged in a scenario like this and puffed up like a balloon. – Michael Hampton Nov 27 '15 at 11:44
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    While you certainly should avoid "heavy duty while charging" due to overheating (extreme situation: A/C power while recording HD video + uploading the stream via 3G/LTE + receiving an alternate stream via 3G/LTE + playing the received stream with your display on full brightness = use gloves when touching the device or you'd burn your fingers: ~6W consumption while ~2W charging), I doubt your "parasitic load" having large effect in "everyday's case" – as otherwise there'd be a fat warning on the cover (or we'd heard of plenty related warranty cases). – Izzy Nov 27 '15 at 13:17
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    @beeshyams Agreed. Though I think this issue is "overrated". I have multiple Android device in use here, some of them for 5 years now, and always charge them while turned on – somethimes even work on them via ADB (USB charging along). Especially the 5-year models are still of perfect battery health. Of course, none of the "duties" applied by during charge are "heavy" :) – Izzy Nov 27 '15 at 14:08
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Yes. Phone does use power from battery when recharging. Although thats something which would more likely depend on how phone is designed, so it may not always be true... but most phones are this way.

I am basing my answer on a test I did. I reduced the charging voltage while at the same time making my phone (my old Samsung Galaxy S3 I9300) use high battery by turning on wifi video streaming, full brightness, volume etc. The battery started discharging more than recharging, and gradually decreased to zero. Soon after battery reached 0, my phone automatically shut down as if the recharger was not connected (it was connected and it started recharging normally after turning off).

Not to mention I wasn't able to run while plugged in without battery.

Again, results may vary.

As for downloading torrents, there will be a slight impact. Because nothing hardware intensive is really going on. You can probably use Android's built in battery monitor to judge if your phone will make it till the download completes or not.

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    Your test says nothing. If your charger was not able to provide enough power for your phone it's obviuos that the phone will take energy from its battery. No test is needed to find it out. – Άνδρας Nov 27 '15 at 10:36
  • @Alex.S IMO that comment suits the question not the answer here. OP simply doesn't understand the obvious stuff, otherwise, the question wouldn't have existed at first place. It is only to explain the obvious stuff that he example was needed. Of course, the poster would explain the situation better here. – Firelord Nov 27 '15 at 13:43
  • It sounds like your charger isn't very good. – SnakeDoc Nov 27 '15 at 17:33
  • @Firelord It is not obvious stuff, battery use while charging is bad for battery health, according to other answers here, so intelligent design would be to no battery usage during charging, and that can be implemented by running device on charger's current. – q126y Nov 27 '15 at 17:37
  • @q126y if that were the case, USB charging would be turned off by default when an ADB connection is detected. Thousands of developers use their devices this way. And as I wrote in another comment: My device with best battery endurance currently is my 2010 Milestone² – which I always charged while turned on. It still uses its original battery. While I write this, it's charge is at 82% – after being on battery (power disconnected) for ~18h today. The only devices I mostly charge while switched off are two of my tablets which I rarely use; one even is almost permanently connected & running ;) – Izzy Nov 28 '15 at 0:14
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Short Answer

  • Is the power consumed from charger or battery to power the device when charging?"- Power is consumed from the charger.

  • "I want to know if my battery will take a hit [while downloading torrents]"- No

Long and Technical Answer

In continuation with my earlier answer quoting Battery University BU-409 Charging Lithium-ion

Noticed that there were other other questions on this site, which directly or obliquely touched upon this aspect of using mobile device /tablet while on charge

Majority of answers leaned towards saying, "it's safe", very few advocating cautious use / advising against using mobile devices at all while on charge. Answers were based on experience and / or technical factoids but lacked an in depth technical justification.

So, here's what I did to try and see how the bad guy "parasitic load"(as explained in my previous answer) troubles us:

  1. Ran tests on using my device (Huawei Honor 6) while on charge with a couple of load conditions to simulate usage (more about this later)

  2. Posted these test results on sister SE Electrical site with a bounty to validate interpretation of results by electrical experts.

  3. Mailed Battery University, requesting their views on the test results. I am extremely thankful to Bruce Huang of Battery University who went through the test results and offered valuable insights and also for permitting me to quote his mail

Test Setup

Airplane mode activated and running apps minimised. OEM charger and charging cable used.

Thanks to @Izzy for the table provided here, used values corresponding to Samsung Galaxy S3, since OP has a Samsung device and results may bear a closer resemblance than testing with Motorola values.

First test was charging, with cell phone kept on (ideally, it should be off as advocated but then how do I test?) and measurements taken using 3C Toolbox. 3C Toolbox was configured to record changes at every 1% change in battery status. More frequent sampling is possible but that would have drawn more power, possibly distorting test results.

Screen brightness was kept at 0% or minimumcorresponding to 567 mW from table.

Second test was with keeping screen brightness at 50% and enabling "Screen will never sleep while charging", in developer options. Reason for choosing this and not downloading follows.

a) Screen on (should) give a stable, continuous load and help catch the "parasitic load" in action.

b) WiFi download consumes 549 mW. Display at minimum brightness is 567 mW and maximum brightness is 1568 mW. Since testing is done at 50% brightness, we can perhaps average it and consider screen load to be 1058 mW, which is nearly double of downloading by WiFi and approximately equal to UMTS download (refer table), since downloading torrents was OP's concern.

Test Results

As can be seen in the linked site having the test results voltage graph looks very different in both cases and I was sure of having nailed "parasitic load" in action. Based on this, logical interpretation was that using the device while on charge for downloading was harmful to battery.

I was wrong in reaching this conclusion, while the tests were correct. I had erred in not looking at the scale (Y-axis) of the graph in both cases, while concentrating on the min and max values, as pointed out by Bruce Huang of BU and @ericnutsch on his answer at the linked site. What this means is that both graphs are pretty much similar and not skewed as it appears.

But this exercise gave good understanding which is covered below.

Conclusions

  1. As brought out in answers on electrical site quoting technical literature of 2008 vintage, it has been the best practice to electrically "isolate" battery and load. what this means is that the charging circuit differentiates between battery and load (here screen power or downloading) and meets their needs separately. 8 years is a long time in electronics and I am pretty sure all major OEM device manufacturers have implemented this if not improved on it as also suggested in the answers of linked site (does this explain why devices are shipped without a warning saying " Don't use the phone while charging ?). And if the load is significant enough, it could impact charging time. Quoting Bruce Huang verbatim

Since the charge current is smaller with screen on, it should take longer time to charge the battery. From the chart provided, I can't tell if the "Constant current charge time" is longer or shorter (he is referring to the current charts in the test results).

To further verify this, I ran a third test. This was also charging with the screen on but the brightness was reduced to the lowest level permitted by ROM. This renders the screen almost opaque. This was to ensure that device is on while consuming least power possible. Pro version of Darker(Screen Filter) permits you to do this . Results:

a) Charging took 5 minutes less than earlier two tests.

b) Voltage and Current graphs were similar to previous tests.

An easy analogy (not technically rigorous) to understand - consider a tap (Charger) connected by a pipe to water a flower bed (Battery). Now you want to fill a cistern (load or using the phone while charging). So you fit a contraption to the tap using which two pipes can be connected independently (electrical isolation). Depending on the size of cistern, it may be filled before the flower bed is watered or may delay the time taken to fill the flower bed.

This answers first part of OP question "Is the power consumed from charger or battery to power the device when charging?"

  1. "Parasitic Load and Current drop". Battery University says

"A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low by drawing a leakage current."

Quoting Bruce Huang verbatim (emphasis mine)

I don't think the parasitic load is going to prevent the current drop forever. I guess the parasitic load only delay the current drop for a period of time. In this test, the parasitic load may be too small (turning on screen with 50% brightness is not huge load) to create a significant delay to the current drop.

This fully explains why the current drop is similar in both cases and not different since parasitic load was not significant enough.

This answers second part of OP question "I want to know if my battery will take a hit [while downloading torrents]"

  1. Does this mean we can do anything with the cell while it is on charge? I am afraid not. Implementation of charging circuit, their tolerances, characteristics etc would vary from device to device and among OEMs. This does not imply you can pretty much do anything when charging. Device specific details being proprietary, are not likely be available on public domain nor provided on request.

Hence, I would not recommend using the cell while on charge for intensive, power hungry applications (just to be on the safer side) using Izzy's table as a guide, if you really care for your battery. Besides keeping your hands off the cell for a couple of hours a day would give you a break too :-)

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I had some phones that I connected to the charger and then removed the battery, and the phone would still work normally as if the battery was inside.

At best, it is possible that you can sustain your whole phone only from the charger, but that is device dependant I think.

Regarding device getting hot while charging and being in use - theres a chip that regulates the current inside, so it's not the battery that is getting hot, its the chip that has to handle charging + discharging at the same time.

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One word answer : "Yes"

Yes smartphones use your battery while in use even when on charging,

But it is not a good practice to use mobile while charging because it Slowly kills your battery life.

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    "But it is not a good practice to use mobile while charging because it Slowly kills your battery life." - please elaborate. Consider adding some credible sources. If possible, cite only the technical ones. While you're on it, consider following How do I write a good answer? – Firelord Nov 27 '15 at 7:59
  • But, the answer is correct and reasonably complete (i.e. warning that using while charging may be bad for battery) . No sources should not be a reason to downvote into negative imho. – Stijn de Witt Nov 28 '15 at 19:42
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There are lots of answers that are right and go into depth. But IMO it can be put really simply in a formula:

Battery = Charger - Phone

I.e. if the charger is putting more current in than the phone is drawing then the battery will still charge (albeit slower than if the phone was off). If the phone is using more current than the charger is putting in, then the battery will drain (and not charge).

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