- 11-08-2012, 11:21 AM #1
Plugging a phone into a wall charger produced heat while charging, which over time degrades battery performance.
Is this the same for wireless charging?
I'm interesting in learning more about this technology and whether or not wireless charging is actually healthier for your smartphone's battery.
It's been said that less time on the wall charger is better for the battery, because it means less heat being generated which reduces overall battery wear. Basically, it's better to 'top off' your phone's battery instead of letting it drain to near empty before charging which generates heat longer.
Does wireless charging help prolong battery life vs wall charging?
- 11-08-2012, 11:27 AM #3
I don't know about the 920, but from my webOS days my phones always seemed to not generate as much heat while wireless charging. The magnetic parts and outside cover (which held the entire system) would warm up, but not the battery itself
Sent from my Lumia 900 using Board Express
- 11-08-2012, 11:36 AM #6
- 11-08-2012, 11:48 AM #7
It's possible to ruin battery life in 1-1,5 years with wrong type of use. With a unremovable battery that can be a problem.
That said, I dont think it matters whether you plug or wirelessly charge, the most important part is to rather charge too often than too rarely. The battery isnt hurt even if you charge it 10 times a day for 10 minutes, it is hurt far more if you let it go sub-10% charge.
11-08-2012, 11:57 AM #9
- 223 Posts
a battery warms up when it is used (discharged and charged), this has no bearing on wall vs induction vs whatever other means there may be to charge the cell.
The rate at which the battery is charged can affect battery life. Fast charging obviously being harsher and resulting in more heat, but it really isn't the heat that's nescessarily the problem (within reasonable limits of course).
It appears that wireless charging takes slightly longer to charge, with that knowledge, it may be slightly more gentle on the battery. But I think both are well into the safe zone where the difference is negligible.
Generally speaking, you can charge any battery at "1C" for maximum safety. where C * mAH = charge amps. so a 2000mAH battery at 1C would be 2A charge rate. Correct me if Im wrong, but I don't think these wall chargers put out more than 1 amp, I know the iphone charger is 1amp.
12-23-2012, 09:17 PM #10
- 58 Posts
12-27-2012, 12:29 AM #11
- 315 Posts
My background so you know where I'm coming from. I'm an Electric Vehicle enthusiast with a degree in Physics. As you can imagine, I want to keep the $5000 battery pack in my car working as long as possible since, unlike a phone, it is quite expensive to replace. As such I have done significant study into the various battery technologies and definitely into the various Lithium based batteries.
While the batteries in my car are LiFePO4 (Lithium Iron Phosphate), the ones in cell phones are typically Lithium Polymer. They have a higher voltage and energy density which is what we want in our phones. In all Lithium type batteries the electrolyte starts breaking down the moment the battery is manufactured. The things that cause it to break down faster is high temperatures and high states of charge. There are other breakdown mechanisms in the batteries too. One of them is Lithium plating and another one is the breakdown of the crystal structure into which the Lithium ions intercalate (where they "park" on charge or discharge). As another poster mentioned, extreme states of charge decrease the life of the battery. Ideally the batteries should be kept between 80-90% and 20% SOC (State of Charge). That would make the battery last a significantly longer period of time. IIRC, Tesla Motors found that charging the laptop batteries used in their cars (Lithium Cobalt) to only 95%SOC extended the cycle and calendar life by a significant amount, 20-50% but I don't remember exactly. Various other studies, including a NASA study I read, showed that keeping a Lithium battery at 100% SOC, rather than charging it up just before it was needed, shortened the life of the battery.
In laptops the batteries rarely die of old age but instead of being held at 100%SOC and elevated temperatures for long periods of time. Time at 100%SOC, heat and full discharges are the killers of Lithium based batteries. Contrary to past practices with NiCd and NiMh batteries, fully cycling a Lithium battery does not make it last longer, it actually shortens its life. I don't know the mechanism used in cell phones to determine SOC so it is possible that a full cycle will calibrate the phone properly so it may give the illusion that the battery works better when in fact it is the electronics which are reporting properly. That being said, there is a slight increase in realized capacity during the first bit of use. You don not, however, have to do any special cycles to gain this increase. Normal use will automatically take care of it so why waste it with a discharging type app? The voltage drop vs. SOC of the batteries used in cell phones is quite steep compared to what I use in my car. This means it is possible to get a reasonable SOC value of a cell phone battery on voltage alone but I don't know if that is what is used. The voltage usually ranges from ~2.7V discharged to ~4.2V charged. (For comparison, the LiFePO4 cells in my EV are ~2.5V discharged and 3.38V charged but the useful range is between 3.0V and 3.38V so very little change. The 2.5-3V range has at most 5% of the total capacity if it is used very slowly.)
What I have found with my Nokia Lumia 920 is that with the Nokia supplied wired charger (rated at 1.3A output) that my battery rarely feels warm, even when charged from a completely discharged phone. When using the wireless charging pad, however, the entire phone gets quite warm even though it is only putting out 0.75A (though I don't know if this is rated at 12V or 5V). Warm enough that I worry that the battery life is being noticeably shortened. I hope to take some surface temperature measurements to see if the temperature is getting into the unsafe range. Basically the battery will be safe below something like 60C (140F) but the electrolyte will be breaking down rather rapidly at that point. I don't even like to see my batteries get much above 30C (86F) but I think with a phone, especially if carried in a pocket or something that it is likely to be that hot quite often. They do best at temperatures that we are comfortable with so on the order of 20-25C (68-77F).
As for heat generation during charging, I have found that the most heat is generated at the end of charge when the battery is nearly full. Very little heat is generated in the vast majority of the SOC range until nearly full. On discharge it is the opposite. Most of the heat is generated near the empty end of the SOC range. If you study the physics and chemistry of how these particular batteries work it makes perfect sense that this should happen this way.
Here is what I have done with my previous 3 phones to make sure the battery easily lasts over 2 years, in the case of my iPhone 3GS it is still going strong well over 4 years later and is in the hands of a new owner. My 2.5 year old iPhone 4 is also still going strong and appears to out last my 2 week old Lumia 920.
- If I am going to use my phone extensively throughout the day where it is likely to be really low by the time I go to bed then I charge it sometime during the day. These batteries do better with many small charges and discharges because it keeps them away from the extreme ends of the SOC range.
- Unless the battery is really low I don't charge it until the morning when I get up. This keeps it from sitting at 100% SOC for very long.
- If my phone isn't fully charged by the time I'm ready to leave I don't worry about it. Stopping charging at 90-95% is actually good for the battery.
- Except in an emergency I do not let my phone get much below 20%SOC and usually try to stay above 40%SOC.
- I don't leave my phone in a hot car or in the sun.
- If my phone were ever to be cooled to below 0C (32F) I never charge it until it has warmed to above freezing. Charging at temperatures below this point significantly increases the chance that Lithium plating will be happening in the battery. Any Lithium ion that plates out as Lithium metal is no longer available to store charge. Discharging at very cold temperatures, however, does not cause any problem, just that the battery doesn't put out energy very fast. This is not likely to be a problem with the really slow rates our phones use the battery but it could be a problem in extremely cold situations.
- If I had the option, I use a lower rate charger which is easier on the battery. I usually use a 0.5A charger for my Bluetooth ear piece if I have the time and my phone doesn't complain.
Hopefully this wasn't too long for my first post but I thought people would like to hear from someone who has a fair bit of personal experience with Li batteries. Believe me, I want my $5k investment to last so I have spent countless hours on the battery care issue.
David D. Nelson
David Nelson's 2003 Gizmo
Last edited by GizmoEV; 12-27-2012 at 12:34 AM. Reason: added last item to list about slow charging
12-27-2012, 03:17 PM #12
- 27 Posts
Thanks, GizmoEV, that's actually very informative and I will try to prevent myself from keeping the phone charged for too long. Your tip is also very useful for preserving my laptop's battery life.
I believe the reason why wireless charging is hotter is because unlike wired charging, more energy is lost as heat during charging (due to imperfect energy transfer). Wired charging has better contact so less electrical energy is lost as heat.
- 01-24-2013, 01:59 AM #14
Thanks for the information, GizmoEV! The Lumia 920 is my first smartphone and I want to learn how to charge it properly and take care of the battery. I've read conflicting information on these forums and on Nokia's forums which has left me confused about what is right (drain the battery low vs. top off often; need to calibrate vs. don't need to calibrate; OK to leave on charger overnight vs. not OK, etc.). One question I have is when the indicator light on the charging plate turns off when charging is done, is the actual charging process stopped? Or is there a risk of overcharging the phone? Nokia's Lumia 920 user manual says not to leave a fully charged battery connected to a charger because overcharging may shorten the battery's life. This plus the information you gave leads me to believe that it's bad to leave the phone on the charger after it's finished charging.
I've just bought the DT-910 wireless charging stand to put on my bedside table so I can use the alarm clock function on my phone. I wasn't sure if it would be OK to leave the phone on it all night, but now I think you've answered my question. It would be bad to leave my phone on the charging stand all night, correct? I think what I'll do is just charge my phone before going to bed, and then disconnect the charging plate from the power supply when I go to sleep. That way I can still use the stand to hold the phone. So far, I've been using the wireless charging plate and I've always removed the phone right after it's done charging, so I'm glad I've been doing the right thing.
I'm also going to follow your advice to charge my phone often and not let the battery charge get too low. I haven't always done that in the past since I wasn't sure if that was the right thing to do (some people say yes, others say no), but what you wrote made sense to me.
- 01-24-2013, 04:52 AM #17
Short charging the battery is better than fully charging it, and fully discharging lithium batteries is not the best idea. Unfortunately sometimes it's necessary to discharge these batteries to recalibrate the electronic battery management system. The system on the 920 has bad programing, or it's simply a bad design. When the battery on any modern electronic device reaches full charge the charger discontinues charging. However the 920 may not do this, if so it's an inexcusable oversight on Nokia's part.
Remember the battery on the 920 is located in the bottom half of the phone. The top of the phone houses the processors, so if the top of the phone is heating up it's not the battery. Batteries are also exposed to elevated temperature when charging on wireless chargers. The energy transfer from a charging mat to a portable device is 70 to 80 percent and the remaining 20 to 30 percent is lost mostly in heat that is transferred to the battery through the mat. Keep in mind that the mat will cool down once the battery is fully charged. Manufactures often overestimate the actual capacity of their batteries, so it's doubtful the 920's battery is actually 2000 mAh.
01-24-2013, 05:25 AM #18
- 64 Posts
According to my opinion, the heating of battery while charging it is normal. It will not affect your battery life. In wired charging, charging many times the battery even if it is not dry reduces the battery life cycle, so charge battery only when its dries up and let it fully charge.
Wireless charging is nice technology and i think its a great start for better future technologies.
Often when we put our wired charger into plug and are not using it, then the electric current is wasted (which is not much noticeable in our bill). But if the same thing is done by millions of people then it is a huge waste. In case of wireless charging it is totally different, if your phone is not in contact of charging pad or you plugs in the charger but not using it, it doesn't use up electricity. That means No Touch, No flow of electric current. that is a nice technology.
Last edited by akashpats; 01-24-2013 at 05:40 AM.
- 01-24-2013, 05:39 AM #19
I see you edited your post. Any wall adapter including the one for wireless chargers wast a tiny amount of electricity, mostly in the form of heat.
Last edited by Andyshine77; 01-24-2013 at 05:52 AM.
01-24-2013, 05:46 AM #20
- 64 Posts
- 01-24-2013, 06:01 AM #21
If the charger has an ac adapter it's consuming some power end of story. What they said in the link you offered is nothing but a lie to sell phones and wireless charging devices. I suppose they may be talking about those who leave their phones hooked up after the phone is charged, other that that the ac adapter is still drawing a bit of power. You're also forgetting the 20 to 30 percent loss, the loss = heat. The loss or inefficiency is way more than the system could ever save.
Last edited by Andyshine77; 01-24-2013 at 06:14 AM.
- 01-24-2013, 07:57 PM #23
I sent an e-mail to Nokia Customer Care (US) to ask if the charging process stops when the indicator light on the charging plate turns off (indicating the battery is fully charged), or if there is a risk of overcharging the phone if the fully-charged phone is left on the charging plate. I got a response today and the rep wrote,
In response to your concern, we would like to inform you that if your Nokia Lumia 920 is already fully charged, the wireless charger will display a one long blink. When the white indicator light goes “Off”, the battery is fully charged. However, if your fully charged phone is still in contact with the Wireless Charging Plate, the charging will still continue.
Please be advised also that the Wireless Charging Plate automatically switches “Off” when not in contact with a compatible device or if it is too hot. You may also turn “Off” your Wireless Charging Plate by disconnecting the power supply from the plate, then unplug from the wall outlet.
In addition to your inquiry, please be reminded that leaving your phone in contact with the Wireless Charging Plate will still cause overcharging the battery. With this, you can only charge your fully drained Nokia Lumia 920 for 4 to 5 hours using the Wireless Charging Plate.
So, leaving the phone on the charger overnight can cause overcharging of the battery. It's best to remove the phone from the wireless charging plate/stand as soon as it's done charging.
- 01-24-2013, 08:23 PM #24
Amazon.com: Energizer Qi-Enabled 3 Position Inductive Charger (Black): Cell Phones & Accessoriesthis one at Amazon and I know it turns off charging when the phone is fully charged. It only starts trying to charge again when I remove the phone and place it back on. But it will end this with a blinking blue light and stop charging. This is how it's supposed to work and I'd be surprised if the Nokia charging plates do not work that way.
- 01-25-2013, 04:46 AM #25
I've been searching through the Discussions forum on Nokia's web site and here's what I found. One user (rayhipkiss) wrote, "The battery does stop accepting charge at 100% but it will start to discharge and when it reaches something like 95% to 98% will start charging again. This is known as bump charging or over charging and can damage the lifetime of the cells."
Then another user (jraduga) gave this further explanation:
"As Ray has mentioned bump charging can cause issues.
when Lithium based batteries were first released, it became very obvious very quickly that they had the chance (as is with many batteries) of going in to a melt down or exploding. as batteries pack in phone are made of many cells all connected, it can only take one cell to go faulty, that then starts a reaction in the pack that cause excessive heat build up, that then becomes so hot that it can cause severe burns or explode. So many years ago they started installing safer types of lithium cells called lithium ion or nowadays lithium polymer cells, they all have a small electronic circuit that controls the charge and discharge rates.
in many cases (not always) the electronic boards even count how many times the batteries are charged, once they hit a certain number they stop accepting charge, this can be as low as 250 times. However this is mainly for many of the older version of these cells.
So bump charging can shorten the life of the battery pack. As ray said it does stop charging but then if it drops enough, it will start again. So where you thought you had charged your battery once, may in effect have been charged maybe 2 or 3 times during a single night. Remember its not the amount of charge you put in, in this case but the number of charges you do.
These circuits are put in for safety reasons, and not to make you buy more of these battery packs. People have had third degree burns to their ears by the use of mobiles in the past, hence why the safety devices were put in."
So what I get from all this is that once the phone detects that the battery is full, charging will stop; however, once the battery drains to a certain level, it will start charging again until it hits 100% then stops. Then this process repeats again once the battery discharges to that specified level again. I think this process of "bump charging" is what is meant by the term "overcharging" in Nokia's user manual statement, "...overcharging may shorten the battery's lifetime." If a battery has a finite number of charge cycles in it's lifetime, then "bump charging" would shorten the lifetime of the battery because it uses up more charge cycles.
So when you leave a phone on the charger overnight, the phone will not charge continuously. It will stop charging when the battery is full, so no worries about the battery overheating and damaging the battery. But what could be bad about leaving the phone on the charger all night is the "bump charging" that can occur, which over time can shorten the lifetime of the battery. Of course I'm not sure to what extent this "bump charging" can reduce the battery's overall lifetime. It may only be a small amount that we'd never really notice anyway. I think this is all starting to make some sense to me.
Here's the link to the thread if you want to read it yourself:
ridiculous... battery lifetime rule - Nokia Support Discussions
On another Nokia Discussions thread, user cjlim wrote, "Ideally you should disconnect from charger soon after charging stops, but doesn't have to be immediately because the phone stops the charging process when battery is full. Not possible to overcharge. However not good to leave it plugged in too long after because top up charging will start if the battery level falls below a certain value."
So I guess the bottom line is that it's OK to leave the phone on the charger overnight if that's what's convenient for you. It shouldn't damage your battery in the sense that it's going to become overfull and overheat. Just be aware that it could possibly use up your battery's charge cycles faster and reduce the battery's overall lifetime. If, like me, you like to err on the side of caution, and can charge your phone while you're awake, then just follow Nokia's advice and take it off the charger when the battery is full.