Battery BMS LED meter

Does the indicator tell you when it is displaying SOC vs. SOH? Or, does it simply determine both and "decide" based on a combination of criteria that may not be visible to you?

No.

Yes, that's what i am guessing.

There are only four LEDs. I guess the user is expected to discard the unit when it cannot be charged up to all four LEDs. So, when the SOH is low, SOC cannot be fully utilized as well.

The unit is 3S9P and usually 50% to 60% overall. Some individual cells are at low as 30%, but no reason not to use them down to 0%.

So, the gauge is actually just a glorified "idiot light" -- not intended to indicate anything NUMERICALLY but, rather a "feel good" sort of display ("We're ALMOST charged...")

Yes, that's what i am guessing. They don't want to explain the difference between SOH and SOC. Depending on site policy, never use without 3 or 4 bars. Also, replacing units before fully depleted.

Someone technically inclined would examine the batteries in more detail. But, for a quick GOODNESS indication, "how many bars do you have?"

The batteries on many laptops have equally dismal (visual indicator) reporting.

Yes, but EV owners are mindful of both SOH and SOC.

Then I would suggest the chosen battery is not appropriate for that market/use.

You have not properly explained this. How do you know there is both SOC and SOH, documentation? Yet it says nothing as to how to know when which is displayed?

I'm not really following what you are describing. I don't know why you worry with such a poorly designed product. Why not use something that works properly?

There are only four LED bars. The manual only says charge to 4 bars before use, and replace battery if less than 4 bars are shown. So, the LED bars are really SOC, except when SOH is low. The BMS will cut-off voltage prematurely.

I guess that include all laptops, tablets and phones. They don't really show you SOH.

Both my cell and my laptop show state of health. What are you talking about???

What I don't get is how you can tell the gadget is showing SoH rather than SoC. Sounds to me like you can't know. I like the idea that it shows SoH when SoH is low. So if you see a low reading, how do you know it's not a good SoH and a low SoC? SoC will change rapidly with use. SoH should only change very gradually with use. If you can't see SoH until it's already "low" (whatever "low" means) it seems pretty pointless.

Wait, "replace battery if less than 4 bars are shown"??? Why would you replace a rechargeable battery just because it's not fully charged??? Are you saying, 3 bars of SoH is "low"?

This is why I hate discussing stuff with you. You never explain anything clearly the first time. It's always a battle getting the info from you.

Mine only show one bar meter: SOC. I have to guess SOH by how long to charge/discharge.

I can measure the voltage (11.2V) when the BMS cutoff from charger.

Some critical (medical) usages mandate 4 bars. Some non-critical usages allows 3 bars. It needs to be replaced because it cannot be charged beyond 2 bars, when the BMS cutoff from charger.

I said it several times that the battery internal BMS cutoff at low voltage when SOH is low.

SoH is just the charging capacity divided by the initial charging capacity. I use a charging app so I don't charge to 100% and it does that division for me.

So you use a voltmeter to check to see if the indicator is SoC or SoH? Maybe you should rig a threshold and an LED to let you know.

You mean SoH? When you say "bars", I can't tell what you are talking about. It's silly for a medical device to care about "bars". There should be a good measurement of battery capacity and the device should request/demand a battery replacement when it gets to some threshold of maximum charge. "Bars" from a battery indicator is not very useful since you don't actually know where the arbitrary threshold is.

Which means what for reading the "bars"? What does "low" mean, one bar, two bars, three bars? You still don't get that you often make no sense, because you don't understand what you have communicated clearly and what you've munged badly. I'm not standing beside you. There's no context to your comments. It matters if you don't connect the dots clearly.

SOH is how much capacity left in the battery.

That's SOC.

If it can't be charged anymore, then it's low SOH.

Low means battery replacement.

Yes, i am planning on that. I can also by-pass the BMS with 12V shunt, but i lose over-current and cell balancing.

2 bars mean it's 50% left. If it can't be charged more than 50%, it has to be replaced in the original medical usage.

One bar is 25%. two is 50%. three is 75%. four is 100%. Sound pretty clear to me.

Measured relative to the original capacity, so "divided by".

It measures both as I explained.

That's not a "low SoH". That's dead.

So, when it shows SoH, it's always zero bars? Got it!

I'm being facetious. This whole thing sounds like it should be tossed and started over.

Oh, so when it has 60% left it shows 2.4 bars? 40% shows 1.6 bars?

If the state were quantized.

There is no fractional bars. I don't really care about the LED bars, but actual voltage level and behaviour of the BMS. The battery can discharge fully from 12V to 8V, charge from 8V to 11V via the BMS and 11V to 12V without BMS. I just wish there is a way to disable the premature cutoff at 11V.