Charging Li-ion batteries to their max voltage - Page 1
Forum section: electronics / projects

author: WillHuang
author_rank: Contributor
timestamp: February 05, 2018, 02:05:32 pm
content: Hi, I was told that if I have a battery that can be charged up to 4.2V, I should not charge it up to 4.2V in order to preserve the battery life. Is this a well known fact? I've been trying to find some resources/papers online about this but to no avail. Can someone point me to a paper that has data on battery life if charged to it's maximum voltage vs charging to jsut below it's maximum voltage (say for e.g. 4.1V instead of 4.2V).Thanks!

author: BravoV
author_rank: Super Contributor
timestamp: February 05, 2018, 02:54:37 pm
content: For longetivity, the sweet spot is 4.0 volt.Watch this ->https://youtu.be/pxP0Cu00sZs?t=1h7m5sEdit : Replaced with YT links at the section where its discussed.

author: John Heath
author_rank: Frequent Contributor
timestamp: February 05, 2018, 03:26:02 pm
content: Post deleted by author.

author: ConKbot
author_rank: Super Contributor
timestamp: February 05, 2018, 04:18:02 pm
content: Quote from: John Heath on February 05, 2018, 03:26:02 pmYeah, don't do that to lithium and don't go around suggesting that other people to too. If it's a protected cell, and you're relying on the protection circuit for cutoff, it's no better than cheap eBay tat, and if an unprotected cell, it's a fire/RUPD/venting waiting to happen. Even if it doesn't it's still destroying cell capacity.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 05, 2018, 04:36:33 pm
content: Quote from: BravoV on February 05, 2018, 02:54:37 pmThat's interesting. I'm just wondering what capacity fraction you actually lose by charging to 4.0 V instead of 4.2 V and how it depends on the battery itself. My guess would be that it would make the actual charged capacity a lot less predictable than going up to 4.2 V and switching to constant voltage, as is usually recommended for Li-ion batteries.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 05, 2018, 04:51:12 pm
content: Quote from: ConKbot on February 05, 2018, 04:18:02 pmI completely second that. This is just disaster waiting to happen. Li-ion/LiPo batteries don't like prolonged trickle charging and will just inflate (for soft pouch cells) and internal pressure will rise. Only very well mechanically protected batteries will remain safe with this kind of treatment. Even with a decent electronic protection circuit, most of these can't do much for protecting against prolonged trickle charging, unless they embed charge counting logics such as in laptop batteries (which need some data exchange and can't be charged with a conventional charger anyway).Of course, if your "trickle charging" never lasts very long in your particular use cases, you may never encounter any such issue. This absolutely doesn't mean that it is safe. What happens if you leave the battery trickle-charging for an extended period of time may not be pretty.As a side note, a given charging current (such as 100 mA in the above example) doesn't mean much without giving the rated nominal battery capacity. 100 mA charging current for a 100 Ah battery may just "tickle" it, so to speak. For a 100 mAh battery, it will probably set it on fire in a matter of a few hours.

author: BravoV
author_rank: Super Contributor
timestamp: February 06, 2018, 08:23:24 am
content: Quote from: SiliconWizard on February 05, 2018, 04:36:33 pmIf I'm not mistaken, at 4.03 volt .. its about 80%. Thing gets worst above 4.1 volt.I marked this at time in this Youtube video where its discussed here below ...https://youtu.be/pxP0Cu00sZs?t=1h7m5sEven though its a 1 hour 14 mins video length, recommending to watch this Prof. Jeff Dahn video from the beginning, its very informative.

author: soubitos
author_rank: Frequent Contributor
timestamp: February 06, 2018, 10:09:16 am
content: A common TP4056 will stop its charge cycle when the current drops to 1/10 of the charging current for a given period. It will also trickle charge the battery if its under 3v when charge cycle starts. And its a common cheap and effective chip. I work with it and TP5100 in my projects. the logic of adding a series resistor to a 32v power supply to charge a lithium battery beats me.. man its not a lead acid battery!!!!! Also if you cannot afford to buy one i will gladly send you one as soon as i get the parts for my next batch of TP4056FlexAdv chargers!!!!

author: BravoV
author_rank: Super Contributor
timestamp: February 06, 2018, 10:15:41 am
content: Quote from: soubitos on February 06, 2018, 10:09:16 amDo you want to add something in this discussion ? Or do you ask something as I don't get it ?Edit : Oh, I get it, you're advertising ...

author: soubitos
author_rank: Frequent Contributor
timestamp: February 06, 2018, 01:16:36 pm
content: Quote from: BravoV on February 06, 2018, 10:15:41 amIf that is your point of view, then yes, i am advertising and you just made it easier LOLOn the other hand, i am honestly offering OP a free charger for his batteries and by telling him that there is no logic in trying to charge a lithium battery with a 32V power supply and a series resistor i hope he gets the point NOT TO DO IT....So, i offer this conversation a piece of advice and a free charger!Can you beat that?

author: Peabody
author_rank: Super Contributor
timestamp: February 06, 2018, 03:11:06 pm
content: Is there a charging I/C that only charges to 80%, or a way to get the TP4056 to behave that way?Also, the TP4056 doesn't exactly trickle charge. As the cell self-discharges, the TP4056 will kick in from time to time to bring it back up to 100%, but it doesn't charge continuously at a low rate because that's supposed to be dangerous. If it is dangerous, then there could be a problem if the project device is powered up while the cell is charging. In that case, the current seen by the charger will never drop to 10% of the full charging rate, and the cell will be exposed to 4.2V continuously. And even if the battery has built-in protection, I don't think that can protect against constant charging at 4.2V.

author: Audioguru
author_rank: Super Contributor
timestamp: February 06, 2018, 04:18:21 pm
content: Half decent lithium batteries are designed for about 500 charge-discharge cycles to full voltage. Go towww.batteryuniversity.comto see how much the capacity is reduced if you reduce the maximum charging voltage.Duh! If you don't charge them but keep them at a "storage" voltage then they last forever but their capacity cannot be used. Most people want maximum capacity and think that 500 charge-discharge cycles are plenty enough.I have radio controlled model airplanes. I charge to the maximum voltage for long flights and lots of power. If I charge to a lower voltage then the flights are short and do not have enough power.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 06, 2018, 05:44:11 pm
content: Decent li-ion cell are designed to be fully charged as per datasheet, still providing rather good cycle life (typ. 500 cycles specified to 70% drop of capacity; often more is actually delivered).Charging to 4.1V (or even lower, it's better, you can go down to about 3.9V after which there are only diminishing returns) increases the cell life somewhat,especiallyif charge currents are high: high current cause most damage at the end of charge. If you need to fully charge at high speeds, you can first charge to about 4.0 or 4.1V at that max speed (for example, 1C), then reduce to a more modest speed (for example, 0.5C).The calendar fading is different: if you want to have an effect to that, you need to drop the max voltage to much less than 4.1V. I'd recommend 3.9V for that. Note that if you are keeping the cell always charged and there is little cycling (i.e., floating a lot), calendar fade dominates over cycle fade, and 4.1V might make no difference whatsoever compared to 4.2V. At 4.0V and below, calendar fading starts to get better, considerably so below 3.9V or even 3.8V (about 50-60%).

author: soubitos
author_rank: Frequent Contributor
timestamp: February 06, 2018, 07:05:29 pm
content: Quote from: Peabody on February 06, 2018, 03:11:06 pmI think somebody suggested adding a diode in series with the battery. This way, they voltage the charger "senses" will be decreased by the forward voltage of said diode... I honestly dont find the reason to do anything other than charge and discharge a battery fully... i mean, if you want to extend a cells lifetime by decreasing its charging voltage you are getting less capacity.. Doesnt matter if its a smaller or bigger amount, it is less... it is somehow lofic if we are talking low maintenance being a key factor and low power demand at the same time.. but i dont really know any carpenter or other professional who would treat his lithium battery powered power tools in a special way decreasing the time he can use his tools per charge even by little instead of getting a bigger battery and using it to its full potential... or someone spending x$ more on a bigger battery only to use it at 80% for example!What should be expected in real life is people NOT trying to charge lithium or any other batteries in ways that could be potentially dangerous to them first and battery/environment second.

author: Peabody
author_rank: Super Contributor
timestamp: February 06, 2018, 09:34:09 pm
content: I don't remember what the OP is using his batteries for. In my case I'm converting my DSO150 kit oscilloscope from mains power to an embedded lipo. But I will have very little need for extended battery life, and will typically have the scope on for less than an hour. So if 4V would make the lipo last materially longer, I could certainly live with the reduced time on battery, particularly since changing it out would require desoldering.As far as I know, nobody makes a 4V charger IC. But maybe if I could rig up a constant current (500ma) circuit with a maximum voltage at 4V, that would work ok. I mean, I assume the algorithm would be the same - charge at a constant current, but switch into constant voltage at 4V, and shut down when the current at that voltage drops below, say, 50ma.

author: John Heath
author_rank: Frequent Contributor
timestamp: February 06, 2018, 11:37:23 pm
content: Quote from: ConKbot on February 05, 2018, 04:18:02 pmAfter reading the posts I understand . I did not realize a trickle charge to a lithium could pose a danger. I take it back. Do not use my cheap charger suggestion. Better still I will go back and delete my post to prevent some one from trying it. Thanks for the heads up.

author: soubitos
author_rank: Frequent Contributor
timestamp: February 07, 2018, 07:39:16 am
content: Quote from: Peabody on February 06, 2018, 09:34:09 pmI think the idea suggested in another thread, to add a schottky diode in series with the battery had exactly that in mind.. if said diode's forward voltage is 0.2V then a charger IC like TP4056 will sense full charge when the battery is at 4V instead of 4.2. The problematic of such a solution while otherwise viable is a. there are not many 0.2V diodes out there and b. those that at least i found are low power (maybe 100mA max) which means you should charge the battery at very low current. Might be a real life solution for small lipo pouches 100-200-400mAh but try charging a 2000mAh battery with 50-100mA and you would stay watching it charging for at least 1 whole day! Note than many battery management/charging ic's have embedded timers which stop charging if it takes over a few hours!Quote from: John Heath on February 06, 2018, 11:37:23 pmThere is no bad question, the only bad one is the one you dont ask... deleting the post means, someone else will not find what was already answered and ask again.. or dont ask and try something otherwise not advisable!

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2018, 06:57:51 pm
content: Most battery types are self limiting, once they reach fully charged any additional power pushed into them is converted to heat, so most types can be trickle charged at a sufficiently low current.Lithium ion cells are not one of these though. If there is a threshold at which the voltage stops rising, it's well beyond the threshold at which the cells burst into flame. Even a low current trickle charge *will* cause a lithium ion battery to catch fire once the voltage rises up to around 4.4-4.5V.