Question storage batteries - Page 1
Forum section: electronics / beginners

author: tiago1986
author_rank: Regular Contributor
timestamp: January 14, 2022, 06:02:52 pm
content: I followed the recommendations and I am storing my xiaomi BM20 and Nokia BP-5L batteries at 3.75v-3.8v but these voltages will drop slowly, at what voltage do I need to recharge them again for storage mode and how long for voltage drop to a voltage that needs recharging?

author: Martin Miranda
author_rank: Regular Contributor
timestamp: January 14, 2022, 06:15:53 pm
content: Quote from: tiago1986 on January 14, 2022, 06:02:52 pmhttps://en.wikipedia.org/wiki/Lithium-ion_batteryyou can store them for 3-4 years without worrying that it would getdamaged(worst case 2.5% per year)but you should recharge it every year and check it's condition, it's still wet chemisty battery. and you need to monitor each battery.

author: Martin Miranda
author_rank: Regular Contributor
timestamp: January 14, 2022, 06:16:49 pm
content: a quick test with a cheap multimeter should do.

author: Gyro
author_rank: Super Contributor
timestamp: January 14, 2022, 06:51:26 pm
content: https://www.eevblog.com/forum/renewable-energy/question-storage-battery/https://www.eevblog.com/forum/renewable-energy/temperature-and-voltage-keep-battery-lipo/

author: tiago1986
author_rank: Regular Contributor
timestamp: January 16, 2022, 08:42:17 am
content: i have and i test multimeter i recharged these batteries a few 3 or 4 months ago to 3.75 or 3.8v and today they are with 3.74v it is necessary for me to keep checking because it can fall too much and damage the batteries

author: Siwastaja
author_rank: Super Contributor
timestamp: January 16, 2022, 08:47:10 am
content: You don't need to check, let them be.Ifthey self-discharge themselves to death, it's only because of them being total crap which would have died quickly anyway.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 16, 2022, 11:37:52 am
content: in the worst case what is the time interval for me to recharge these batteries? clone of xiaomi BM20 batteries (seller said it is original) and clone Nokia BP-5L

author: Gyro
author_rank: Super Contributor
timestamp: January 16, 2022, 12:31:40 pm
content: 7.35yearsdaysweeksmonths.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 16, 2022, 12:58:02 pm
content: Quote from: tiago1986 on January 16, 2022, 11:37:52 amWho knows? Your question does not make sense, because:* If the cells are decent, there is no such time interval. They keep just fine. Maybe you can check the voltage every 3-4 years to be sure?* As the cells are counterfeit crap, anything is possible, the worst case is they burst in flames any moment and burn down your house. Unlikely, but you asked for worst case.Let them sit, and if they die on their own, let them die.

author: SilverSolder
author_rank: Super Contributor
timestamp: January 16, 2022, 02:49:50 pm
content: Quote from: tiago1986 on January 16, 2022, 08:42:17 amLithium-Ion batteries stay at a flat voltage for a long time, they don't start dropping until they go very low.It doesn't hurt to check them (it uses almost no energy to check their voltage), for your peace of mind.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 16, 2022, 06:36:54 pm
content: i really don't know the quality of these batteries they seem good some 2 or 3 or 4 months i charged them to 3.8v and today they are in the 3.73v range but i don't know when to charge and how long to recharge them again

author: Siwastaja
author_rank: Super Contributor
timestamp: January 16, 2022, 07:15:08 pm
content: Quote from: SilverSolder on January 16, 2022, 02:49:50 pmI don't think the curve you posted is a really representative example. I have never seen such curve in any real-life cell, but something close to that might exist of course.Consumer cells are more likely nearly not that flat; look for practical examples athttps://lygte-info.dk/info/indexBatteriesAndChargers%20UK.html(Lowest current graphs are quite close to open-circuit voltage). Most are surprisingly linear between 100%-25% and then drop faster, and this is also my observation on testing ~15-20 different cells (mostly LCO and NCA).

author: Siwastaja
author_rank: Super Contributor
timestamp: January 16, 2022, 07:19:05 pm
content: Quote from: tiago1986 on January 16, 2022, 06:36:54 pmMeasure again in January 2023 and report back.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 16, 2022, 07:46:39 pm
content: do they hold a charge for 1 year without risk of damage and me permanently losing the batteries?

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 16, 2022, 11:00:04 pm
content: If they don't hold some charge for a year they weren't very good to begin with.Something everybody should learn to accept is all rechargeable batteries are inherently limited lifespan devices. Some types/chemistries destroy themselves (lose capacity, gain ESR and self discharge) faster than others, but to the best of my knowledge they all do it, perhaps with the exception of stuff like the old school flooded lead acid motorcycle batteries that give you a bottle of acid to pour in at the time of installation, but that just gives you control over when the timer is started. Attempts at rejuvenation, meticulous long term storage, etc. are mostly a waste of time. Charge them full, put them away (ideally in a steel box away from flammable materials), and forget about it for a year, recharge any that are still above the minimum safe voltage (3V I think?) and repeat.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 17, 2022, 12:06:57 am
content: Fully recharge 100%? above 3.8v?

author: SilverSolder
author_rank: Super Contributor
timestamp: January 17, 2022, 01:28:59 am
content: Quote from: Siwastaja on January 16, 2022, 07:15:08 pmI have only experimented with small li-po bag cells, and they behaved (as a rough approximation) like the curve below at very low rates of discharge. Leaving the batteries in the fridge is as low a rate of discharge as it gets!It is pretty difficult to tell the state of charge of a LiIon cell from its voltage when it is in the midde of its range.

author: Munyua44
author_rank: Contributor
timestamp: January 17, 2022, 04:41:32 am
content: the batteries can be stored for over 3 years without getting damaged but it could be good practice if you recharge them every year to check their conditions.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 17, 2022, 02:06:25 pm
content: charged in 3,8v or full 100%?

author: SilverSolder
author_rank: Super Contributor
timestamp: January 17, 2022, 02:23:02 pm
content: Somewhere around 50% is the least stressful for the batteries.See attached document, it seems to answer most of your questions from a practical perspective.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 17, 2022, 05:31:47 pm
content: Quote from: SilverSolder on January 17, 2022, 01:28:59 amPackaging (pouch, prismatic or cylindrical) is unrelated, curve shape is defined by the chemistry (and microscopical details in anode / cathode construction), for example synthetic vs. natural graphite in anode makes a difference.In any case, leaving the cells anywhere, fridge or not, means zero discharge rate which obviously leads to constant voltage. Did you actuallymeasure(by logging voltage vs. integral of current) the curves of said cells, or did you just get the feeling they kinda match the graph your posted? Serious question, because I have never seen cell that is nearly as flat, but differences are indeed large so onemightexist. Ignoring LFP cells, every cell I have tested has been easy to map between open-circuit voltage and SoC. Of course, in presence of large load variations that becomes more difficult to do exactly.The example is also for the 4.35V (3.8V nominal) LCO chemistry, this is quite a rarity today. The only 4.35V cell I have tested wasn't flat, but very linear like all tested 4.2V LCO cells.

author: SilverSolder
author_rank: Super Contributor
timestamp: January 17, 2022, 06:09:11 pm
content: Quote from: Siwastaja on January 17, 2022, 05:31:47 pmI guess I was thinking mostly about the general shape of the curve: that there is a quite long stretch around 3.7 Volts where the voltage doesn't change as much as it does near the beginning and the end. The curve is good enough to see the gist of that.I did test the cells - but only the voltage, not the current - precisely because I was trying to estimate how long they would last while self-discharging on store shelves! I did encounter long stretches of relative flatness around 3.7V.My conclusion at the time (several years ago now) was that they could easily stay charged more than a year in normal temperature conditions, if charged to 50% at the factory. The problem was to isolate them well enough (FET leakage currents was a problem - not much of an issue in the fridge, although the protection circuits do eat some tiny amount of energy).

author: Siwastaja
author_rank: Super Contributor
timestamp: January 17, 2022, 07:49:03 pm
content: Oh, OK. My guess is that you measured them at 3.7V for a long time only because they simply were not self-discharging, so the SoC kept constant, you were at a single point in the curve. Self-discharge of li-ion cells is often overestimated. I have measured between 0-10% of capacity per year, around 3-4%/year being typical at room temperature, and this is for a full cell. At 3.6-3.7V, self-discharge is between 0%-1% per year.Linked is a typical example curve from lygte-info.dk:Notice how different this is compared to the Silicon Lightworks example? You can easily see the SoC from the voltage exactly because the curve does not have a flat area. Straight line fit between 4.15V and 3.2V does good job giving 100%-5% SoC, and you can leave 5% for the birds.But yeah, some are flatter, but Silicon Lightworks example seem pretty extreme!

author: SilverSolder
author_rank: Super Contributor
timestamp: January 17, 2022, 08:14:44 pm
content: Quote from: Siwastaja on January 17, 2022, 07:49:03 pmThe curve is flat enough that estimating the State of Charge based on voltage is challenging. Basically, the open circuit voltage of a Lithium Ion battery is not a very precise indicator of the SoC.People have done all kinds of desperate things, up to and including Coulomb-counting to try to better keep track of the SoC.E.g. see this article:https://www.lithium-battery-factory.com/lithium-battery-state-of-charge/This whole area is a minefield!

author: tiago1986
author_rank: Regular Contributor
timestamp: January 18, 2022, 01:15:19 am
content: i charge for 3,8v what self discharge per year?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 18, 2022, 08:48:43 am
content: Quote from: SilverSolder on January 17, 2022, 08:14:44 pmI don't know, I do this for a living and for me, it has never been challenging, but works well and is simple.Of course, the indication jumps around a bit with load changes.Coulomb counting is more challenging to get right, but nowadays it usually works well (in laptops etc.) During the first decade or so, problems with severely jumping indications were usual.

author: SilverSolder
author_rank: Super Contributor
timestamp: January 18, 2022, 01:04:45 pm
content: Quote from: Siwastaja on January 18, 2022, 08:48:43 amWhat you say is interesting - the voltage can be "good enough for Australia" to estimate the charge level?What happens as the battery ages and the cycle count begins to rack up, and it begins to lose capacity - surely you must lose a lot of accuracy as time goes?

author: Siwastaja
author_rank: Super Contributor
timestamp: January 18, 2022, 05:29:14 pm
content: Quote from: SilverSolder on January 18, 2022, 01:04:45 pmVoltage-based SoC indication adapts automatically to the capacity loss without any action. OTOH, if due to aging internal resistance of the cell increases, indication jumping due to load variations also increases. Voltage-based indication works best for fairly low-current loads (i.e., when under-load voltage is not too far from open-circuit voltage.) Short peaks are not a problem - just filter the reading.Voltage based measurement is notoriously bad on NiCd, NiMH and lead acid chemistries because of their flatness, and works quite well in Alkaline primary cells and most li-ion chemistries. It would work very poorly with the Silicon Lightworks example cell, but again, I suspect this is a made-up curve (or some special snowflake cell).Coulomb counting needs to track actual capacity, which requires reset points, which are voltage based anyway; usually full and empty. If battery is not regularly fully charged, coulomb counter drifts, lacking 100% reset point. If battery is not regularly fully discharged, estimate of actual capacity is not updated. If you want to make truly useful coulomb counter (without requiring the user to do full charging/discharging cycles), you need to really incorporate voltage and current measurements all the time, along the curve, so it would be a fusion of integrating charge, and estimating from voltage. I would guess the best "fuel gauge" ICs do this quite decently nowadays.OTOH, there are also ICs that incorporate "advanced" algorithmswithoutcoulomb counting, but still utilize information about voltage, current, and the pre-programmed cell curve. This allows near the accuracy of coulomb counting, without the cumulative error, and without need to fully discharge the cell to estimate actual capacity.

author: tiago1986
author_rank: Regular Contributor
timestamp: January 18, 2022, 10:45:27 pm
content: Should long term storage of these batteries of mine be at 100% charge or 3.8v?

author: gnif
author_rank: Unknown
timestamp: January 19, 2022, 11:29:43 pm
content: Quote from: tiago1986 on January 17, 2022, 02:06:25 pmQuote from: tiago1986 on January 18, 2022, 01:15:19 amQuote from: tiago1986 on January 18, 2022, 10:45:27 pmYour question has been answered! What is with this spam?You're being watched...

author: tiago1986
author_rank: Regular Contributor
timestamp: January 21, 2022, 06:00:37 pm
content: My doubt was not answered about which voltage drop I need to charge these batteries again so they don't have a shortening of their useful life

author: Siwastaja
author_rank: Super Contributor
timestamp: January 21, 2022, 06:04:08 pm
content: You "need" to recharge if they go below 3.0V.That being said, if they do that on their own, it's only because they are broken anyway. Charging them could be dangerous. So really, if they get below 3.0V on their own, just dispose.

author: Gyro
author_rank: Super Contributor
timestamp: January 21, 2022, 08:47:48 pm
content: Quote from: gnif on January 19, 2022, 11:29:43 pmReply #3 in the following link will probably help you then... he's been here before, several times.https://www.electronicspoint.com/forums/threads/electrolytic-capacitor-doubts.295396/#post-1816504

author: tiago1986
author_rank: Regular Contributor
timestamp: April 08, 2022, 01:56:59 pm
content: Is it true that the best long term storage of removable lithium and lipo batteries is at voltages between 3.75v - 3.85v? i have xiaomi BM20 and Nokia BP-5L batterieswhen the load in storage drops what value of load drop do i need to recharge these batteries again for storage voltage?

author: CaptDon
author_rank: Super Contributor
timestamp: April 08, 2022, 05:45:34 pm
content: Good God are you dense in the head?How many times will you ask the same question??? No one can tell you EXACTLY, it depends on the quality of your batteries. You have asked the same question and been answered dozens of times. Charge them to 3.8 volts. They will last for years, but they obviously won't last as long as your endless rambling thread asking the same question on different forums!!!

author: Gyro
author_rank: Super Contributor
timestamp: April 08, 2022, 08:01:34 pm
content: He seems to be displaying a Belgian flag now, I'm sure it was Brazil last time!

author: MK14
author_rank: Super Contributor
timestamp: April 08, 2022, 08:06:50 pm
content: Quote from: Gyro on April 08, 2022, 08:01:34 pmIf it is a Belgian IP address, then I assume they are trolling and using a different VPN exit node country.Alternatively, if it is a Brazilian IP address (still), I assume they are trying to hide the fact they have already been permanently banned from this Forum, on umpteen occasions.Either way, they are effectively SPAMMING the same or almost identical questions all over the place. Which is usually against the rules.