back to article 'Charge memory' boffins: Hungover Li-Ion batts tell fat whoppers

The widespread belief that lithium-ion batteries don't suffer from “charge memory” might be mistaken, according to new research out of Japan and Switzerland. The research, published in Nature Materials (abstract), finds that “charge memory” can emerge in the common electrode material lithium-iron phosphate (LiFePO4). As a …


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    1. Anonymous Coward
      Anonymous Coward

      Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

      Presumably Petr Novak sells battery management software.

      What I've read about Li batteries is that the cardinal sin is to run them completely out. Anyway; the memory effect is minuscule, according to the article.

    2. Stacy

      Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

      Actually, I have quite the opposite from Sony... The battery management software recommends that you only charge to 80% (if you are close to a socket most of the time, which I am) in order to extend the life of the battery - as 100% charges kill the battery over time.

      1. Nick Ryan Silver badge

        Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

        From reading the engineering rags relating to this kind of technology, the most damaging thing to do to these batteries is over charging. There is a very big difference between the cheaper and and the more expensive charging control circuits.

        To reduce the risk of charge memory (aka tide marks) the majority of modern software controlled battery management systems have a charge threshold where they don't charge a battery when it's past (e.g.) 97% full unless it started below that point. This prevents the device from charging to 100%, running down to 99%, then charging to 100% and so on.

        The other big problem is judging the scale of battery capacity itself. The tech and monitoring for this has is still improving all the time and in itself requires quite complicated management software to track the changes over time and even consider environmental factors in order to reliably produce an even close approximation of the real battery level.

      2. Number6

        Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

        Li-Ion batteries suffer a loss of capacity over time, and that loss is worse at 100% charge than at lower charge levels. Most batteries are shipped with about 40% charge because that gives a good compromise between shelf life and loss of capacity. If the battery manages to fully discharge it can start gassing and explode/expand, so it needs to start with enough charge for a six month shelf life.

        Leaving your laptop plugged in and sitting at full charge is going to cause it to lose capacity at a higher rate than leaving it at 80%, so certainly Sony have that right.

        1. Dave 126 Silver badge

          Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

          My Sony phone had an option to stop charging at 95%- though it seems to have disappeared with the ICS update. Back in pre-iPod days, it was Sony who put more effort into promoting their portable audio players as being 'premium', and claims of quick charging often formed a part of it.

      3. DJ Smiley

        Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

        That's bad battery design.

        The batteries physically expand as they charge. If they expand so much they become compressed they can be damaged. If their casing is so small they can't charge to full size? BAD DESIGN.

        Then again it's Sony.... so I'm not too surprised.

      4. zb

        Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

        My Samsung Chronos laptop has a setting in the BIOS allowing the user to set a maximum battery charge of 80% to prolong the life of the battery. It seems to work very nicely. I disable the setting when going on long trips and keep it at 80% most of the time.

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        1. Stacy

          Re: @ Stacy @...Pierre

          What you said:

          Mind you, the _manufacturers_ advise full cycles to avoid charge memory

          What I said:

          The battery management software recommends that you only charge to 80%

          Since when is charging to 80% the same as a full charge cycle?

          Your situation:

          Wait till it's nearly empty (10%) and charge to 100%

          My situation: It's on 65%, I plug it in and it stops automatically at 80%. That is not a full charge cycle.

          Not the same thing. In fact, quite opposite.

          1. ElReg!comments!Pierre

            Re: @ Stacy @...Pierre

            ha, it appears that "full cycle" may have different definitions. Also, you make a lot of asumption on my battery use...

            In fact, appart from your quite wild and ungrounded assumptions, it appears that I am ideed 100% correct, and that you may not be completely wrong yourself (appart from the 65%-80% thing. that's just stupid, and you just invented these, obviously; depending on the gizmo that kind of percentage is 1/2h to 6 h autonomy, nothing tthat anyone would be willing to advertise these days).

            1. Stacy

              Re: @ Stacy @...Pierre

              I know I shouldn't but...

              Mind you, the _manufacturers_ advise full cycles to avoid charge memory

              From this I assumed that you meant a full cycle of nearly empty to full. If you could explain what you mean by full cycle without attacking me I would appreciate it. I used the information presented to me.

              My figures were taken from the air yes. Sometimes my battery is nearly empty (warning! your laptop will hibernate if you don't plug in soon!) and needs charging to 80% (when the Sony battery application stops charging). Sometimes it's not and when it plug it in is still has 65% left and charges to 80%. And a whole range in between. I don't wait for my laptop to hit 65% and then charge it, obviously. That would be just a little to much OCD for me.

              As for the % left on *whatever* I am charging, I take it from the machine itself. The laptop reports x% charge left, as does my phone. The hours left? That depends on what I am doing. Writing mails takes less processing power than photo editing obviously and so the time to empty changes with current power needs. As a singular example.

    3. Stevie Silver badge

      Re: The widespread belief that lithium-ion batteries don't suffer from “charge memory”

  2. Herby

    People compared to

    Older chemistries. Back in the day, when NiCd batteries were in full bloom, everybody talked about the "memory effect", which works out to a similar process. Lithium batteries were the "solution" to the problem. Now it turns out that the problem exists in Li based batteries as well.

    So, back to the drawing board. Or, can you build me a better battery charge management solution (most likely microprocessor based).

    1. Flocke Kroes Silver badge

      First dix the problem, then find out what was wrong

      Battery memory was a popular diagnosis for any reduction in charge retention no matter what the real cause. It is much easier to blame battery memory than to actually find out what the problem is. Here is a simple test for memory effects: Is the battery in orbit and charged by solar power? Without that precision repetition of charge cycles, you should be looking elsewhere for the cause of reduced battery performance.

  3. quartzie

    Blown out

    As interesting as the title seems, just looking at the graph shows that the *dreaded* memory effect is in fact minuscule in Li Ion batteries.

    Talk about blowing a story out of proportion. Among the problems facing Li-anything batteries, memory effect is hardly worth mentioning.

    Re: Pierre, I noticed that the general public is very prone to parroting any 'seemingly true' facts about technologies they don't understand. Do yourself a favor and check some actual research before believing everything in your first google search.

    1. Rampant Spaniel

      Re: Blown out

      Well said! I think the original 'no memory' effect related to the fact in comparison to nicads and to a lesser degree nimh, li ion batteries have 'virtually' no memory effect. If you look really REALLY hard there may be a small one. You used to have to nurse nicads, discharges, slow full recharges etc and even then their life wasn't exception. Liions are a hell of a lot better, they can charge quickly, be recharged plenty of times and don't seem to care that much about their state when you charge them. They don't last forever (although I have a canon 10d original battery somewhere that still works if anyone wants to figure out how old that is!) and they take a hammering. 1000 recharge cycles seems to be about the norm with some cells easily 50% higher. This just seems to be pedant fodder.

      1. Don Casey

        Re: Blown out

        Canon 10D - introduced 10 years ago

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  4. Anonymous Coward
    Anonymous Coward

    I wonder if it is charge memory or something else

    that makes my iPhone 5 sometimes charged up at 100% in the morning and after a half hour of constant use still show say 98%, but other times it drops below 100% almost instantly after I begin using it? There have even been a few times I've started the day at 99% despite having it on the charger for 4-6 hours. Either there's some extra charge above what is reported as 100% that I sometimes get and sometimes don't, or my varying patterns of use during the day averaging over 50% charge remaining when I plug it back in at night are causing some charge memory.

    In the past month on days when I've used it lightly and was over about 65% at bedtime I've avoided plugging it in to allow a deeper discharge on the next day. A couple times I got it down to single digits. When I recharge after being down below 20% it seems to be more likely I'll get one of those "100%+" charges, but it isn't guaranteed.

    1. Tom 35

      Re: I wonder if it is charge memory or something else

      The %charge display on a phone is not exactly accurate. I expect what you are seeing is more likely due to the charge display then the actual battery.

      1. MrT

        There was a recalibration trick...

        ... that HTC recommended for original Desire owners though, so it seemed the battery management software waw being fooled about what was '100%', rather than the battery chemistry itself.

        IIRC the method was to charge to '100%' with the phone on, then turn it off and charge for another hour, then switch it on again for another hour's charge, then unplug and restart the handset. On mine, it used to yield around 10% more usable life, which gradually faded again over about 2 months if the phone was just charged whilst left on. I've only tried it once on my GS3, which doesn't seem to be as prone to this.

        Mind you, since the software is designed to protect the battery from damage by overcharging it may have been set a little over-cautious by HTC.

    2. TeeCee Gold badge

      Re: I wonder if it is charge memory or something else

      Well, both my Sony phone and Acer tablet came with statements that this was to be expected and it depends on when in its "fully charged" cycle you disconnect it.

      Their charging circuits charge the thing fully, then allow it to discharge a tad, then top up, etc ad nauseum, to avoid shagging the battery by overcharging. I suspect that Apple do the same but don't want to confuse their sheep with the nasty technical stuff....

    3. Number6

      Re: I wonder if it is charge memory or something else

      That can be a function of the charge algorithm as much as anything else. The battery get to 100% and the charger cuts out. It then waits for the battery volts to drop slightly before attempting to recharge. If you take it off charger just after it cuts out then you do have 100% charge. If you take it off the charger just as it's about to turn on again, you might only have 98%. NiCads usually ended up on trickle charge, and so were always at 100% once it had been reached.

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    1. Danny 14 Silver badge

      Re: Switch off data

      you can get reasonable software that will detect throughput and cycle the process automatically for you. I use "easy battery saver" which lets you get a threshold (such as 5k in 5 seconds etc) if the threshold is met then it powers on the data and powers down after a preset time.

      Same for bluetooth and GPS (powers on only when needed etc).

    2. MrXavia

      Re: Switch off data

      Interestingly when I was abroad with an SGS and no local sim, I turned off everything but wifi, set wifi to run all the time and installed a sip client, in that arrangement I get about 3-4 days standby (and checking emails etc, no gaming or media playing)

      Yet on 3G, I get only around 1 day standby with similar usage when always in range of a base station, if I was to travel with my phone, I loose 20-30% battery life due to loss of coverage.. It seems to me that mobiles are not designed to work in citys where you often walk in and our of coverage...

      1. Dr_N Silver badge

        Re: Switch off data

        3G is (still) notorious for sucking up battery life. Especially if you have push email active etc.

        In which case you actually get better battery life if you have the WiFi on/connected all day at work/home.

    3. Craigeena

      Re: Switch off data

      I had an HTC Hero as my first android phone. Great at the time, but terrible battery. After I replaced it, I tried a little test to see how long the battery would last with everything off:

      Normal use: 2-3 hours (battery was a bit shagged).

      Airplane mode, with 1 screen switch-on per day for a few seconds to check if it was still alive: 13 DAYS!

  7. John Tserkezis

    Careful with the terminology...

    The NiCad "Memory Effect" (the REAL one) can be a challenge to reproduce, and requires a good set of very repeatable conditions for you to see it. And even then, what it *actually* does is very different from what "everyone" claims. I even have great doubts as to the odds of seeing the Memory Effect (again, the real one) in a domestic environment (cellphones, torches, toys, whatever). Ditto for NiMh, which were claimed to be entirely immune.

    Yet, every man and his dog saw the memory effect appearing for both. Except they didn't. Voltage depression, when coupled with the ever popular and the plethora of variations of dVdT methods of end of charge detection, meant everyone became an expert on diagnosing charge problems.

    The fact that the Memory Effect (yet again, the real one) appearing in a variety of different chemical based energy storage devices is not surprising, more so when gauging on how rare it is.

    So, it's not the end of the world guys, it's actually quite unlikely you're ever going to see it at all.

    1. Danny 14 Silver badge

      Re: Careful with the terminology...

      what most people thought was memory effect was usually because they had overcharged and overcooked the batteries leading to them venting and simply not charging up to full any more. cheap chargers that kept pumping mA into the batteries killed them rather than "memory effect".

      1. Chairo

        Re: Careful with the terminology...

        cheap chargers that kept pumping mA into the batteries killed them rather than "memory effect"

        Yes, and the only reason why Li-Ion chargers don't do this, is that Li-Ion batteries tend to blow up if overloaded. Otherwise we would still be stuck with the cheap, crappy charging circuits that killed off generations of otherwise perfectly rugged and reliable Ni-Cd and Ni-Mh batteries.

  8. Kevin McMurtrie Silver badge


    Most effects are seldom noticed because the battery stays within normal tolerances. I've found that the charge history has the biggest impact when running the batteries at high currents. It's not always the classical memory effect, but how material in the battery packs together or crystalizes. For example, a NiCd race car battery that has been partially discharged, idled, and then slowly recharged puts out maybe 1/3 the current of one that was run dead and rapidly recharged immediately before use. SLAs have similar issues with how the sponge lead forms. Finding documentation on this is tough and experimenting on lithium batteries means destroying them (and maybe other things nearby).

  9. ilmari

    Oh dear god, please no

    Now everyone will be blaming memory effect for everything

    ... "I installed 50 background apps, but only 49 of them use gps and 3g, and I'm not sure about the 50th, what's a bitcoin miner do? Anyway, now my battery doesn't last anymore??? Can't be the apps, must be memory effect!!"

    ... "I left my phone empty in a drawer for a month after I droppped phone in beer, and now battery life sucks. I opened up the phone and attached the battery to a car battery charger for a week, but that didn't help, so I borrowed a medical defibrillator and gave the battery repeated shocks, but memory effect is just getting worse and worse, halp!"

    In all seriousness though, if you take someone very familiar with typical Li-Ion batteries such as LiCoO2 and similar, which we have in phones and computers, and tell them LiFePo4 is "just like" LiCoO2 but explosion-proof and lower voltage. it takes just one charge cycle for them to discover that LiFePo4 behaves nothing like traditional LiCoO2. When I first got a LiFePo4 batterypack I immediately noticed that charge behaviour was quite different. I couldn't find much litterature on the subject, except vague nonsense about "forming charge", and a somewhat competent looking research paper that used xray microscopy to compare slowcharged batteries to fastcharged batteries (where fast was on the order of 10 minutes), the findings being that fast charge caused less wear and tear.

    Anyway, the point being that there's only one laptop ever (OLPC), and no phones at all, that have used a LiFePo4 battery. Considering how different LiFePo4 is from what's actually used in laptops and phones, this memory effect is entirely irrelevant for the normal user, even if the discovered effect wa s bigger than 1/1000th..

    1/1000th is ldudicrously small anyways, considering battery meters in phones andsuch often are off by 20 percent or more... That also means it's nearly impossible for regular users to draw any meaningful conclusions from how they charge and use their devices, as there's no accurate measurement of drain and charge level, and the zero-point often jumps around from cycle to cycle.. Zero-point being the charge level at which the phone considers itself empty..

  10. mANgLEr

    I have a filthy mind

    That graph is just low brow graffiti.

  11. JeffyPooh

    Seriously, who cares?

    Okay, if you own a satellite in geostationary orbit then you'd want to wake up in the morning and worry all day about your Li-ion cells. If you own an electric car with a Li-ion battery pack, you certainly wouldn't want to charge it above 80% nor allow it to discharge below 79%, because the resultant 320-foot range of this battery-conserving approach should be plenty enough for anyone.

    For the rest of us with laptops and cell phones, who cares? I *just* replaced a 5.5 year old laptop battery pack for about $27 (all-in, delivered). I spill more dollars in coffee than that. It's just not worth worrying about. Provided you know how to shop on-line for replacements, and have a modicum of good luck or good planning.

  12. Hayden Clark Silver badge

    Multi-cell battery crapness

    I think that most "memory effect" moans are actually the degradation of battery capacity due to cell damage. When a series stack is deep-discharged, the lowest-capacity cell will get reverse-charged. This damages it, so that the next time the stack is discharged, the runt cell gets reversed-charged more.

  13. Rick Brasche

    In the radio control and EV world,

    we have always been warned against depleting a lithium based chemistry battery. Problems with cell balance and "venting with flame" were significantly reduced when our speed controllers automatically shut down before any cell in a battery gets too low.

    In other words, "Never Go Full Discharge". :)

  14. Anonymous Coward
    Anonymous Coward

    Its interesting to note

    That "totally dead" ie won't charge LFP cells that sit at about 2.2V no matter how long you charge them for can sometimes revive if you heat them up to about 80C for an hour then charge them.

    Not sure what is going on here, can someone suggest why heating would have an effect?

    NB: Don't do this to Li-CoO2 or anything other than LiFePO4 cells...

  15. JeffyPooh

    "Be a consumer, not a curator." - a very wise man

    It's a lot more relaxing.

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