Real-time cells voltage display instead of BMS

Hi,
As I manually balance my A123 20Ah pack for 4 years, and as they slowly age, I wanted to have an onboard voltage monitor which shows all 24 cells at the same time. I already have a big handle-bar bag which is secured firmly and I have plenty of surface area on it to mount any voltage grid matrix.

I thought to achieve the task with Arduino but it's rather complicated (especially due to common ground issues), and so I opt to simplify the matters in several options:

1. Buy one of those Chinese battery checkers which show 6 cells at the same time. I will need 4 of those:
https://www.aliexpress.com/item/4000078311123.html
https://www.aliexpress.com/item/4000078311123.html
I know those have their own "Chinese" issues but they come off-the-shelf as one package. Still, no seller could confirm the voltage range for those, so I know if they can be used with LiFe and not just LiPo.

2. Buy 24 self-powered (to avoid the dreaded common-ground issue) volt-meters:
https://www.aliexpress.com/item/32601434804.html
They are rated down to 3V, while the LVC can be as low as 2-2.5V. I assume they can go lower than 3V, but no Chinese-seller answered my question about it.

3. Most reliable, simple, and can be turned off easily - One volt-meter and one 24 position 2 pole rotary switch. I can watch only one cell at a time, but since I know the battery very well, I can monitor the weaker cells and dial the switch as needed.

4. Perhaps you know about a compact voltmeter that fits my demands? (and I will buy 24 units of it...)

5. A battery voltage checker that instead of 6 cells (the max I found) can show 24 at the same time? (and naturally it would be bigger..)

6. An Arduino shield off-the-shelf product that is designed to read the analog signal of 24 cells (or more) in series and outputs digital data?
(I am not gonna design one myself or fool around with operation-amplifiers. This will end in a disaster...

Looking forward to your thoughts about this.
Thank you!

The good old cell log 8 has been discontinued. This looks like a nice replacement assuming they get them back in stock. It does LiFe and balances which is cool since the old cell log used to pull the cells out of balance over time. Its nice that you'd only need 3 instead of 4.

https://www.progressiverc.com/cellmeter-8.html

Since you know your pack well and just want to be able to know when that first cell falls off the cliff at 3V, and you run an even number of series cells, have you considered just running 2 voltmeters (one for each half of the pack)? Then when the 2 voltages become different, you'll know a cell is low. 2 cheap voltmeters and 2 switches is all you need, which is far easier monitor than trying to look at all 24 voltages on the go.

John in CR said:

Since you know your pack well and just want to be able to know when that first cell falls off the cliff at 3V, and you run an even number of series cells, have you considered just running 2 voltmeters (one for each half of the pack)? Then when the 2 voltages become different, you'll know a cell is low. 2 cheap voltmeters and 2 switches is all you need, which is far easier monitor than trying to look at all 24 voltages on the go.

Click to expand...

This is a very nice idea and it's better than the current situation (monitoring only the pack voltage), although it's not perfect since after a continuous load of high discharge current the cells take up to few minutes to recover the voltage due to the hysteresis sag. I assume, that some cells recover faster than others.
What is your impression about this phenomena, by the way?
When you have an individual cell voltage map, you can watch this in realtime, and perhaps have another forecast approach to weaker cells. This, in fact, can only be monitored if you watch all cells at the same time and see which recover the slowest.

Since those 6 cell monitors are quite cheap, perhaps they are a good option after all.
I will place a multi pole switch to each of them, so I can turn them on when needed, so they don't slowly drain the battery. (and unevenly - only the first cell is used to power the monitor, as I saw here on ES)

How about just getting a 24S BMS with LCD? If you don't want to use the BMS function, just disable it via the app or PC software, and just use the voltage display functionality.
https://h5.aliexpress.com/item/32847177119.html

I cant speak for all cheap cell monitors but with the cell log 8s disconnecting just one wire to turn them off still resulted in uneven drain on the cells. The only way to prevent the drain was to totally disconnect the unit from all the wires.

serious_sam said:

How about just getting a 24S BMS with LCD? If you don't want to use the BMS function, just disable it via the app or PC software, and just use the voltage display functionality.
https://h5.aliexpress.com/item/32847177119.html
24S BMS with LCD.jpg

Click to expand...

Looks nice but to pay 170$ just to monitor the cells is too much
And the whole point is that I find BMS's to be not trustworthy so I would also need a multi-pole switch to disconnect all the cells from the unit when not being used, and switches to bypass the BMS's main leads when not in use.