🔋Lithium vs. Lead Acid: Voltage vs. State of Charge (SOC)

[@philbrooke-little7082]

The chart is a rested and stable voltage chart it isn’t claimed to be able to give SOC when charging or discharging. BMVs are renowned for being incorrectly set up and for ruining lead acid batteries by people believing them. The problem is them not being synched correctly, having the wrong percentage efficiency set, the wrong tail current, the wrong charged voltage, particularly where solar is part of the mix. The best SOC meters use a combination of coulomb counting and rested voltage as rested voltage can be used to correct the SOC indication when he coulomb counter isn’t being regularly synched with a full charge. Resting voltage charts are actually very useful for showing when BMVs are out of sync and I would say they are an essential check against being misled. You just need to know what they are intended for and use them as such.

[@kpd3308]

You are entirely correct. This video is misleading. Anybody should know that battery voltage will be depressed during discharge and elevated during charging. Resting voltage is the key.

[@Z-add]

Can you point to a video that explains this correctly

[@reginaldpotts2037]

No matter what chemistry a voltage chart won't be accurate when a load is being applied to the battery, you have to let the battery rest a while with zero charge/ discharge. Even so, it is more difficult with LFP to ascertain SOC by voltage because the curve is so flat compared to FLA.

[@Andy-df5fj]

Isn't that chart resting voltage, not under load voltage?

[@JonathanWinterflood]

yes, yes it is...

[@freelectron2029]

yup. this guy has all the gear and no idea. welcome to the internet.

[@robertmuster1350]

So many people purchase and install LiFePO4 (LFP( batteries and use Lead Acid battery gauges to meter capacity by voltage. The voltage curve of LFP batteries variation is so small, that even at rest, does not give a true indication of capacity. The best capacity measure is using a meter (that is set at full capacity) and a shunt to measure amp hours extracted from and added to the battery.

[@Andy-df5fj]

@@robertmuster1350 I agree. The best test being a loaded test is actually true for lead acid batteries as well, at least for general battery health. The issue with loaded tests is that the voltage chart would only be at a very specific load (1C, 2C etc) and with the wide variety of battery capacities, would require a variable load tester and more knowledge/skill to perform the measurements. A simple voltage reading is quick and easy, albeit not the most accurate.

[@dantronics1682]

@@freelectron2029 We'll never know if he has any idea or not but I think he was just trying to sell a named product

[@ruan2587]

uhm..so where is the lead acid comparison as per your title?

[@bearchow1929]

Your title is wrong. You didn't discuss lead acid at all.

[@thomashardin911]

He is also wrong about the voltages, you can discharge a lfp4 battery to 11v and there is data to prove that, if you’d like…

[@boklingvicente1460]

Right, no lead acid battery tested

[@GabrielSBarbaraS]

Almost seemed like a shunt battery monitor commercial instead of talking about Lead acid batteries

[@MrHugemoth]

30 years ago I installed a Bogart Engineering cumulative amper hour meter and 500 amp shunt. Its still working after 30 years of 24/7 use. That was on a lead acid battery bank. Just switched to lifepo4 where it also works well at showing state of charge.

[@dantronics1682]

Now considering that a shunt is just a piece of metal, what could go wrong with it?

[@Sylvan_dB]

Problem is there are at a minimum 3 voltage:state curves: Under charge, under discharge, at rest for at least 30 minutes. In reality, LiFePO4 voltage is nearly uncorrelated with state of charge.

[@josepeixoto3384]

i find Lifepo4's Voltage to represent their SOC with precision; i have 40 lifepo4s(old, CHEAP, 20 of them donnated from non use etc...,some bought USED...) arranged in a 48 volt system working off grid for 2 years nowm i build my own LOW FREQUENCY inverters using the MODDED EGS002 famous control board, only 5 or 6 euros; oh.. and a 3000 watt 23 kg toroidal trafo and the 47microHenry coil of course the voltage is WITHOUT FAIL the SOC, because i KNOW my batteries by now; they are Amazingly Very Consistent.... what a chemistry!!! i just look at the current, in or out, or near zero, and go from there; i know them all, immagine you have 5 or 6 dogs for a while, you´d know them too.

[@Sylvan_dB]

@@josepeixoto3384 Nonsense. If you give you a battery there is no way you can measure the voltage and know the state of charge. You cannot change physics. I've had LiFePO4 batteries for 10 years (and lead acid for decades before that). A 100% full charge on LiFePO4 can be anywhere from 13.5 to 14.6 volts, depending on how long the charger has been turned off. If you are currently charging or discharging the curve is entirely different from each other and from an idle battery. While charging or discharging there is only 0.1v difference from 20% to 80% and less than that if the battery is idle.

[@josepeixoto3384]

@@Sylvan_dB physics? i am an engineer, and i know that ALL lifepo4 manufs, say to rest the cells 2 to 4 HOURS before measuring the volts; i install small home off grid systems, and i modify and build (solar) inverters, and when you rest the lifepo4s, the volts are the SOC then ( it used to be in the lead-acids, the DENSITY is the SOC,you spotted a weak cell right away, but now they are sealed, no can do..) the lifepo4 curve is NOT flat, you just need a voltmeter that measures to 0.01, and this almost all do, you have then from 3.40 down to 3.00, or 40 points of SOC,never fails; one GETS USED, just by eye, to correlating the VOLTS to the CURRENT, ascending or descending, i use a simple strap-on induction amp meter 10 bucks, not very accurate, but does the job; BMSes are no nonsense, and work on VOLTAGE, how would that be possible then? edit; i do have coulomb counters, simple amp-hour integrators (like the PZEM-015) but there is no need for all those fancy gizmos on my installations, OTHER factors are MORE important, like SUN, PANELS, BATTERY; intagrators i use for Cell Capacity Tests only.

[@50kArchipelagos]

Very helpful. Thx. New owner here. Odd observations explained in that vid. Charger vs. voltmeter vs. display vs. blabla. I'll feel better with the right compensatory readouts. Will do.

[@Maherashraf89]

Brother what is the lowest voltage for the gel batteries because I want to adjust the control device to disconnect on the least voltage so that no overdischarge occurs and the battery life decreases

[@jimhanty8149]

Good vid… I don’t see how anyone gets by without a good shunt .. I love my V- 712…

[@jasonbroom7147]

I have not used either of these Victron shunts, but the problem I've run into with some of the other products is they do not measure smaller draws very well, especially the current an inverter draws while it's on but not powering a load. The end result is you think you have close to 100% SOC, but as soon as you start powering an actual load, that percentage drops very quickly. Do the Victron shunts handle this any better? The problem with what is shown in this video is you're only showing the voltage of the battery while under load. While that is probably a good real-world demonstration, it's somewhat disingenuous because LFP batteries DO show a gradual voltage drop at lower SOC, but you're obfuscating that by having it under a load. Also not mentioned is your 100AH battery won't be a 100AH battery forever...which means if you want an accurate reading from the shunt, you'll have to capacity test and recalibrate the shunt periodically. Most people get way too hung up on knowing the exact SOC of their LFP batteries. Keep them charged up to 80 or 90% and add more capacity, as you are able.

[@josephhartman2343]

Thanks. Very helpful. I have a an expion battery monitor with expion 360 lithium lithiums and was concerned as my voltage was moving from 13.3 down to 12.5 and still showing plenty of amp hours and 100-90 SOC. This makes total sense.

[@50kArchipelagos]

It looks like a LiFePO4 can last twice as long if you don't run it below 50%. Is that true?

[@s.mendez7160]

Not true. Temperature, and not over charging, or pushing small amounts of current into an already charged battery - using float mode on LiFe battery are what will shorten the life cycle count.

[@50kArchipelagos]

@@s.mendez7160 Thx.

[@loganv0410]

WHOA Big Fella. The chart, though horribly wrong as you say, is based on resting voltage. Neither of your curves are, nor can be by the nature of charging and discharging, at resting voltage. I heard you say that you discharged at 50A. What was your charge current? Ah - you're selling coulomb counters.

[@HighTechLab]

Who, in the middle of using their batteries, shuts everything off for hours "to rest" to figure out how full they are?

[@Andy-df5fj]

@@HighTechLab No one. But many will measure a resting battery to determine its state of charge before using it.

[@curtchase3730]

@@Andy-df5fj That's one thing about lead/acid batteries. Voltage droop is a big thing. The harder the load, the lower the voltage. It sounds crazy, but, yes, in order to get some idea of the SOC of a Lead/acid battery, the load must be disconnected for several minutes at least, then measure the terminal voltage.

[@goodman854]

yeah sales pitch, lol.

[@michaelmedicworldoftanks33fps]

​@@Andy-df5fj exactly

[@last2minutes587]

where is the lead acid? subject says lithium vs lead acid.

[@keithej2]

I have two 12V 100 Ah and they are very different voltage wise. The one with Bluetooth varies the voltage a lot as it discharges. The other battery voltage changes very little from 100% to 20%. In my experience, the AGM voltage chart reflects SOC much better than the LiFePo4 charts.

[@CurrentConnected]

If they are at different voltages, it's best to charge them both fully that way they can balance out.

[@SoutheastOhioSolarHaven]

100 % You have no Idea how many people have argued Battery Voltage is right for Lithium. Lithium Batteries are a different chemistry and monstrous Storage !

[@WG7D]

Isn't that chart just for lead acid?

[@chadjones99]

yes

[@CurrentConnected]

No it is shared on many websites, forums and Facebook groups as for lithium. With lead acid resting full charge is at 12.8v

[@WG7D]

@@CurrentConnected Thanks for clarifying!

[@Sylvan_dB]

@@CurrentConnected With lead-acid the resting full charge is 12.6v. This is a major reason why you cannot parallel lead acid with any lithium chemistry.

[@Sylvan_dB]

@John-Nel Sure, connect them. Charge them full. Disconnect the charger and all loads. What happens? The LiFePO4 with a higher resting voltage of 13.3 to 13.4v will keep float charging the lead-acid above its resting voltage of 12.6v until the LiFePO4 is discharged to 12.6v (at LiFePO4 at 12.6v is well below 50% charged). Then the lead-acid will continue to self-discharge as it does, and the LiFePO4 will go right down with it. Congratulations, you have achieved the worst of all worlds. Why do you think you could fight physics?

[@rondhole]

ONe thing that is very important. Lead acid battery must be above 11.7V all the time before it start degrading from sulphation problems. The Lithium is the other way around, it degrades rapidly if it is close to fully charged.

[@CurrentConnected]

For lead-acid, yes, you are correct. For lithium, not so much. With NMC and NCA chemistry, they do have additional internal stress and degradation when at high state of charge, but for LiFePO4 (LFP), they do not have this issue! In fact, most LFP BMS modules only balance when the battery is at 100%, so by not charging to 100% you get additional degradation and capacity loss from cells being out of balance.

[@thedolphin5428]

​​@@CurrentConnected Nonsense. "Most Lithium BMSs" (with active balance) can be programmed to balance at any value, but 13.4v is considered good. I recently discharged mine to 10.5v whereupon cells were way out of balance. So I set it to active balance ALL THE WAY UP to 100%. What is the point in ONLY top balancing?

[@chris_mk5supra]

these voltage are for the battery resting, not when it's drawing energie ... witch WILL make the voltage drop. i mean ... DUHHH

[@louf7178]

I take the chart to be for resting voltage, which is after 2 hours, which is a big condition.

[@vevenaneathna]

ugh victron. i love how viction charge controllers require you to destroy them if you want to open and replace a fuse or capacitor thats blown.

[@landonferguson7282]

What shunt do you recommend for budget builds? Is there one that's cheaper than the 130 dollar victron smart shunt, or is that the cheapest reliable option.

[@CurrentConnected]

Victron SmartShunt is the lowest cost & most reliable option we suggest. While some cheaper ones do exist, they certainly are doing it at the sacrifice of accuracy and features.

[@landonferguson7282]

@@CurrentConnected I'm very happy with my smart shunt, just wondered about other options. I wish the smart shunt had a simple and low cost screen that connected to the 4 pin port on the shunt, to display the information. The cheapest option for a display I've found is to use a used tablet as a screen for it.

[@CurrentConnected]

That tablet is a very expensive screen! For this use case, we have the BMV-712 that only a few bucks more, but it has its own screen you can mount up to 25 feet away for viewing at a quick glance.

[@landonferguson7282]

@@CurrentConnected I got the tablet for free, otherwise I wouldn't get one.

[@Noah-qt3rq]

The Bogart Engineering trimetric shunt is also quite good, just doesn't have bluetooth. I used it before I got the Victron

[@neail5466]

Man you are focusing that much on charge voltage but taking the capacity rating as granted !! The device should see some charge and discharge cycles and determine the true capacity. Plus you have plotted the graph on a discharge cycle, that obviously drops the voltage but when you charge the (considering its not floating then the charger will be supplying the power needed, and voltage will not drop, considering provision overhead in that in the charger) but at the charging cycle the voltage shall rise in ball park of that charge. Your point is right when calculating the backup time but probably not when considering charging, still, in that device capacity should be varified through the program.

[@josepeixoto3384]

Not so with me; you may read my (reply to comment below); from 3.200 to 3.330 you have 130 points to id the SOC,and that is enough; i disregard all methods, except the VOLTS; of course, i correlate to the amps (in ,or out, or near 0), and then, Volts are SOC; i am so used to my 40 cells, on a 48 volt setup, all used, mix and match!!! working well for 2 years, i kind of know them all 16 arrays,one by one now.

[@erictstahl]

Great video. Thank you.

[@NigelM18]

Interesting, i have a 24v 50ah battery i setup with the infamous chinese shunt and i wanted my battery resting at 80% thats supposed to be 26.65v and the shunt was telling me i was only at 72.6%....... this vid is making sense of it now. I just upped my chage to 26.7v I'll see where the shunt settles now and keep adjusting till i hit 80%

[@vroor32]

What shunt is that? My shunt won't show the SOC on lithium...😢

[@dantronics1682]

Did anyone explain that a shunt is just a piece of metal? It doesnt matter if its chinese vietnamese or indian. its just a bit of metal with a known resistance

[@NigelM18]

@dantronics1682 yeah sure the shunt is just metal but not the electronic controller that's supposed to monitor that piece of metal. Victron vs Chinese..... big difference.

[@dantronics1682]

@@NigelM18 Yep Big difference £200:£40

[@50kArchipelagos]

So I guess you want an led readout never letting it go below 12.9? if you can't afford the 130.00 shunt.

[@Science-Vlog]

thanks for this nice tutorial

[@ИванИванов-м6ч1о]

the chart is for OCV. I wonder how a dude with a rackfull of expensive test equipment doesn't know that. And current measurment also is not 100% accurate

[@gerrymcerlean8432]

That shunt must waste a lot of battery capacity. It is constantly converting electrical energy into heat. Doesn't seem like a great idea to me.

[@CurrentConnected]

Not at all. At 100A load it's less than a watt.

[@bwigmytch]

Lead acid on the title

[@cowboymcq6711]

I’d love to hear a tech from signature solar explain 100 ah batteries LMAO That company is an absolute joke steer clear of them ‼️‼️‼️

[@MrTyroneweaver]

Go Burley Bobcats

[@bethalpha]

. Amazon chargers will destroy lead acid