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.

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.

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.

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.

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

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.

thanks for this nice tutorial

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.

Great video. Thank you.

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

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

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

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

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 !

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

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%

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.

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.

Isn't that chart just for lead acid?

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.

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

Go Burley Bobcats

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 ‼️‼️‼️

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.

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.