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I have read recently that frequent top-off charging of my personal electronics is hard on the batteries. Specifically, Li-ion batteries in recent model smart phones and laptops will show significant loss of capacity after (very roughly) 300 cycles between the remaining charge levels of 90% and 100%.

Below is a 'cartoon' of a plot to help clarify my question. Is cycling between the 90% and 100% points 'harder' on these types of batteries than an equal number of cycles between the 40% and 90% levels?

By 'harder' I mean a significant loss in battery capacity after (very roughly) 300 cycles, versus maybe 3,000 cycles.

Also, is cycling through the lower end (say 5% to 40%) also 'harder' than in the mid-range?

I'm not looking for opinions or best guess - I need a fairly clear answer with a link to further reading, and ideally an actual plot of this phenomenon - model or data.

edit: assume the charging is managed by the built-in electronics according to manufacturer's specifications.

NOTE: This question requires an engineering answer, but let's assume I am not so much of an engineer (anymore) that I have actually taken my phone and laptop apart and I'm hooking up volt meters to the individual cells!!!

Please assume I am simply either plugging into a power source, or not plugging into a power source, the way most people do, based on the 0-100% scale that my personal consumer electronic device displays.

Thanks!

cartoon battery cycling

uhoh
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    I'm not going to put forward a well researched answer, just enough comment so you can google for the relevant things. It's not charging *through* the top 10% that does the damage, it's the length of time spent warm *above* 4.1v, where lithium starts to go walkies. That's why chargers don't continue to trickle charge like you can with lead or nickel chemistries, they stop charging to allow the voltage to fall and spend most of its time below 4v. – Neil_UK Apr 30 '16 at 09:09
  • @Neil_UK thanks for the helpful info - 1st I have to change the title, 'through' is an unfortunate choice of words. Also, implicit in my question (which I'll also edit to make explicit) is the assumption that the charging is well managed by the associated electronics as recommended by each battery manufacturer. I just don't know how to say '*top off charge*' in engineering-speak. – uhoh Apr 30 '16 at 09:16
  • See batteryuniversity.com | Here is your definitive answer :-) : Topping at 90% is fine IF you do it properly. | NEVER apply more than 4.2V, Charge at Imax until 4.2V reached. Imax is usually C/1 but see data sheet. | At Vbat = 4.2V swap to CV (constant V charging). Ichg will taper down under battery control. Stopping at Ichg = Imax/2 will give you the large majority of capacity. | Stopping at Imax/4 gives more capacity and more stress. | Stopping at Imax/10 is for road warriors and beats the stuffing out of your battery. | Reducing Imax to say 4.1V increases battery cycle life. .... – Russell McMahon Apr 30 '16 at 12:51
  • Stopping at Imax/2 improves cycle life. || NEVER NEVER NEVER trickle charge once end of charge cycle is reached. – Russell McMahon Apr 30 '16 at 12:52
  • Here is a "reference" for [**more reading**](http://electronics.stackexchange.com/search?q=user%3A3288+liion) :-). – Russell McMahon Apr 30 '16 at 12:53
  • @RussellMcMahon Your comment is incorrect and certainly not "definitive". What is your source for this incorrect info? Even if done "properly", such topping off causes more degradation because higher voltages and temps accelerate various internal parasitic electrochemical processes. Since this dependence is *nonlinear* (often exponential), even small changes in charge termination voltage / capacity can lead to large increases in life. To maximize life you should minimize the time the cell spends at high temperatures and extreme voltages. – Bill Dubuque Apr 30 '16 at 13:11
  • @RussellMcMahon I already added "*assume the charging is managed by the built-in electronics according to manufacturer's specifications* ." a few hours ago. Assume I am simply either plugging into a power source, or **not** plugging into a power source, the way most people do, based on the 0-100% scale that my personal consumer electronic device displays. – uhoh Apr 30 '16 at 13:11
  • @BillDubuque To have the sort of conversation you seem to propose we'd have to better define his, my and your assumptions sets. To start with. I assume he is wanting to have his system as near to full capacity as reasonably possible on random occasions so that if he needs to suddenly use it away from a charging source he gets maximum run time. In such cases, maximising charge termination current and dropping Vmax by maybe 0.1V will get him substantial gains in cycle life while largely meeting his needs. | Minimising time at "extreme voltages" is hard in his scenario as if he desires ... – Russell McMahon Apr 30 '16 at 13:22
  • @RussellMcMahon and move to chat possibly, rather than here under my very first (and in fact carefully worded) question that ever asked in this particular Stack Exchange site? – uhoh Apr 30 '16 at 13:23
  • ... 90% charge Vbat will always be at Vmax. | The question needs to be more detailed to get into a more detailed answer. | FWIW LiIon tends to increase total Watt.hrs of delivered charge as depth of discharge per cycle decreases. eg for say 10% DOD and 20% DOD cyles you will get mot=re than 2x as many 10% DOD cycles as 20% ones, all else being equal. – Russell McMahon Apr 30 '16 at 13:25
  • @uhoh There are old studies by NASA that lend some support to the claims that you've read recently. However, it is not clear if these old results transfer immediately to modern cells because many improvements have been made since then. What exactly is your goal? Are you trying to devise a charging schedule that maximizes the life of your cellphone battery? – Bill Dubuque Apr 30 '16 at 13:29
  • @BillDubuque my goal is to get an answer to this carefully worded question. If there something there that is not clear please let me know! I'm asking about the deleterious effects of charging - at different fractions of total charge - on the overall capacity of the batteries. This is really the question for which I would like an answer. It seems that some people are wishing that I was asking a different question, to which they could answer 4.1 volts! Alas, I'm not. – uhoh Apr 30 '16 at 13:53
  • @uhoh It is difficult if not impossible to give a precise answer because that would depend on much context that has not been supplied, e.g. the exact chemistry of the cells, and various environmental context such as temperature and humidity during charge and discharge, and the type of load (pulsed or not), storage times, the health of the cells (e.g. internal resistance), etc. – Bill Dubuque Apr 30 '16 at 14:00
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    @uhoh I think you will increase your chances of obtaining a useful answer if - instead of posing the problem in the abstract - you add some background motivation that explains how you plan to apply this information. – Bill Dubuque Apr 30 '16 at 14:05
  • @BillDubuque thanks for your advice. I'll wait a day or so, and if no helpful answers are forthcoming I'll edit it accordingly. I appreciate your follow up, and I'll do the same. – uhoh Apr 30 '16 at 14:09
  • Help us out. Where did you recently read that the 10% DOD schedule is bad for the battery? Maybe you misunderstood what you read. No offense intended. That happens here a lot. – user57037 Apr 30 '16 at 18:20
  • Well, if my old hp laptop is anything to go by, it's spent around half its 4 year life plugged in and was drained on a regular basis and it still holds just as much charge as when I got it. Some batteries are better than others and so tend to survive much longer - the hard part is sorting out which is which – Sam May 01 '16 at 00:18
  • @mkeith thanks, I have been trying to find it for sure. I stumbled upon it while rummaging around in the less-reliable nether-worlds of consumer electronics advice. I *thought* it was in Wired (which *usually* gets their engineering info correct, from reliable sources) about recent iPhone batteries, but I can't find it exactly in that form. I'll keep looking, and if I find it I'll add it here. – uhoh May 01 '16 at 01:43

1 Answers1

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Yes, fully charging and discharging the battery will result in lower lifespan. The difference is not 10 times, but it is significant.

Here are some example plots from Kokam. For the 80% and 20% tests every 50th cycle was done at 100% (the vertical red lines) to check the full capacity.

At 100% charge/discharge the capacity dropped to 97% after 300 cycles.

At 80% it took over 1500 cycles. This is 5 times more cycles, but closer to 4 times improvement since only 80% capacity was available per cycle.

At 20% it managed 3000 cycles. This sounds impressive, but since only 20% of the full capacity was extracted it is equivalent to far fewer than 3000 full charge/discharge cycles. Depending on how the device being powered uses the available voltage and capacity, it may even be worse than cycling to 80%.

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The main reason that a Lithium-ion battery 'wears out' is stress caused by expansion and contraction of the active material as lithium ions are squeezed in and out. Limiting the amount of charge/discharge reduces the expansion/contraction amplitude, which lessens damage to the plate material.

However, even if a lithium-ion battery is held at constant state of charge the plates will still degrade due to oxidation. This occurs faster at higher temperature and voltage, so keeping your battery cool and at less than full charge will increase its shelf life.

For a device such as a laptop which is usually used on mains power, it is better to run the battery down a bit and (if possible) remove it until it is needed. A device which is left unused for long periods should be stored with the battery partially discharged, and not recharged until just before the next use.

Bruce Abbott
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  • This is *exactly* what I was hoping for, thank you for taking the time to find data which is so graphic and quantitative *and* to summarize it so well! The distinction between number of cycles and total excursion in relative charge (%) is important to interpreting the data, and you've explained it clearly, along with the mechanisms and interplay of temperature, and of charge level during storage. – uhoh May 01 '16 at 01:47
  • Hmm...so it's not a constant total energy over the life of the battery. (simple sum of all charge/discharge cycles) If it were, then most of this would be moot. – AaronD Aug 11 '22 at 01:16
  • Also, I think the graphs are misleading. At first glance, it looks like they're discharging the battery to 80% or 20% *remaining*, denoted by the red line, when they're actually testing the top 80% or 20% *capacity* and leaving the rest. – AaronD Aug 11 '22 at 01:18