weird issue with low battery the other night

So basically my batteries ( one or more ) dropped to around 5 or 6 volts the other morning, let me explain more, I am staying somewhat full-time in my RV, and I have 5 ( in parallel ) Lithium 100Ah batteries (12-volt system ) . My inverter ( a go-power IC 3000 ) has a low battery cut off I believe around 10.5 volts, and if you know RVs you know your DC loads go direct to the batteries, so we ( this is what I think happened ) were running the heaters ( furnace 12 volt Dc system ) all night ( off and on ) and when I woke up we had no power, I thought no biggie Ill fire up the generator and the inverter will start to charge the batteries. (the sun was not up yet so no solar yet ) I got the generator going and I could not get anything online, the inverter would not even go into pass-thur mode, I notice my DC stuff was acting weird, like the TV sound bar LEDs were blinking on and off, so I pulled up my Victron App and also went to the inverter display panel and it was dead, long store short I seen we only had like 5 volts on the shunt reading, I cycled the inverter switch a few times then it went into pass thru and we got AC loads off the generator but still no DC power, I had to go get my car plug-in battery charge and jumper it onto my buss bar then once I got the battery up to around 6 plus volts I could get the charger in the inverter to kick on and start powering DC loads and charging. What threw me off was even though my DC loads ran the batteries down I would think my BMS,s on the batties would have cut off by 9 volts not 5 or 6 , and maybe some of them did, can tell if all 5 were at 5 volts or one did not shut off and other BMS,s did?
just wondering how much damage I did to my lithium batteries or which even one didn't isolate ...
normally I don't have an issue with losing power at night with 500 AH , but we had the batteries down to around 32 % the day before and not much sun, and I did not change them up enough.
Also since then, I have added a low-voltage audible alarm to the system.

We full-time. One item I added to my system is the Victron Smart Battery Protects. BP-65.

These go to my fuse panel. (My inverter has a different path - so it works for my system). Power can only go one direction through these - no charging.

I have them set to cut-off at 11.6v.

So in my system the lights, heater, etc. cuts off at 11.6v the inverter cuts out about 11.2v (residential fridge is on that). Then the bms cut-outs below that.

That way hopefully the bms never has to activate the low battery cutoff.

I would disconnect the batteries from each other and get a voltage test on each battery- make sure they have all woken up and charged.

This may also give insight into which bms failed its cutoff. I would consider that battery very suspect to failure.

Also the cells in the battery that failed are very likely to be VERY unbalanced when fully charged. I would get a bms replacement, then top-balance those cells.

Good Luck

Also, you need to occasionally (annually) do a battery capacity test to make sure you still have 500ah of capacity. My guess is you don’t - which is part of what caused the issue.

If your test shows 478Ah’s - be sure and reset your battery monitor for the new lower number.

yes I agree I need to do some type of capacity test, at the time I had less solar on it and I was having a hard time living off the grid getting enough energy to charge them up past 65% during the day, but now that I've added another 600 watts of solar and my wife is out of town ( she doesn't turn stuff off, she will go outside and leave the TV on, you can't do that when your off grid & trying to top off your system ) it has been charging up to the high 90 % range( the only load right now is a full size fridge ) , I'm out of town too so when I go back up ill reset the Victron shunt once I get them charged all the way up to where they don't take a charge and run them down and meter the AH,s out through the shunt ( to 10% i don't wanna run it flat anymore). But like you said before I test ill disconnect all the batteries and do at least a voltage check on them all to make sure none are offline.

I use to have a BP-65 a few years ago on another RV but smoked it somehow, I did not add one to this system being it is a 12-volt system, it draws a lot of amps when running loads like the microwave,etc I might could add a BP-220. I did add a few passive items to alert me if the system gets too low, one is an audible alarm ( made for boat battery I think) that will go off if you go above 16 volts or below 11.6 and the other is an emergence light that comes on if you lose AC power ( I.E. inverter trips on the low voltage it will wake me up and I can fire up the generator ) , but since I added the extra solar panels I have not had any more close calls on low voltage ..( most mornings I'm still at 45 % or more and only ran it flat that one morning, I woke up and notice all the power was off. but I just couldn't believe it went all the way down to 5 volts .

For the cutoff range - pick something voltage wise that makes sense and you won’t change.

For me I picked my inverter running about a 700w load. Ran the system down until the inverter shutdown the first time and called it a completed test. The voltage rebounded and the inverter turned back on after 15 seconds or so. But I called the test completed.

I had just DIY my battery bank. Purchased Cell capacity said 544ah, I got 525ah and so I set that in my battery monitor. (There was still power left in the cells). After one year I dropped the battery monitor to 500ah. I need to re-do the capacity test myself and see how the battery is doing.

On the BP-65. Can you just run everything except your inverter through it? The inverter has its own low voltage disconnect. This way everything has some kind of low power disconnect- even if you are not there.

your right the line the leaves the bus bar on my system goes to the RV breaker box then the DC loads while the inverter has its own line off the bus bar, So I can put it on the line that goes to the DC loads and use the smaller BP-65. good idea

Rocketman said:

Also, you need to occasionally (annually) do a battery capacity test to make sure you still have 500ah of capacity. My guess is you don’t - which is part of what caused the issue.

If your test shows 478Ah’s - be sure and reset your battery monitor for the new lower number.

Click to expand...

So I tested battery capacity today, I got 511 AH when the inverter shut down ( set to 10.7 volts ) and my DC loads were still going. I did add a Victron BP-100 and have it set to cut off at 10 volts but I'm going to bump that up to 10.5 next trip in the side box of the RV. So I did get more than 500 AH not sure how much more but did not feel a need to cycle them that hard. I reset my shunt reading and I am now charging back up ( will take all day )

chadjones99 said:

and if you know RVs you know your DC loads go direct to the batteries,

Click to expand...

Everything should go thru the BMS. Isn't your BMS at/on your battery?

You really should consider your BMS to be part of your battery. This will greatly simplify what you need to do throughout your entire system to ensure your battery is protected.

MisterSandals said:

Everything should go thru the BMS. Isn't your BMS at/on your battery?

You really should consider your BMS to be part of your battery. This will greatly simplify what you need to do throughout your entire system to ensure your battery is protected.

Click to expand...

LOL where do I start .... of course, I have A BMS I have 5 BMS,s each battery ( battle born ) has a built-in BMS..
the reason I talked about the inverter dropping out at 511 AH in , and me still having DC power is because the power leaves the battery ( going threw the built-in BMS ) and goes to a bus bar , then the inverter takes its supply and powers my AC loads, the RV fuse box also feeds off the bus bar but before I install my BP 100 ( a few days ago ) the RV DC loads would not cut out on low voltage before the BMS disconnected on low voltage ... And so now I have a BP-100 that will cut off ( I hope ) right before the set point on the battery BMS In case I have one of my 5 not cut off. because a few weeks ago I was running my heater and the fan ran the batteries down to like 6 volts ( but know I have read that when a battle born cuts out on low voltage you will still read 5 volts output ) so I may or may not have cut out I don't want to trust the BMS alone so I added a BP-100 on the line going to the RV DC loads only not the inverter mainly because I would need a very large BP model higher than the one they make ( I think they go up to 220 amps )
I tested the battery capacity today on inverter shut off at 10.7 volts and pulled 511 AHs and could have gotten more if I left the DC loads on and pulled down to BP-100 cut off or BMS which ever came 1st but I didn't want to stress the batterys