Victron Smart Lithium Battery Imbalance

[AgentOneee]

Hi there,
I got two brand new Victron Smart Lithium Battery 25.6V 200ah and plan to connect them in series to build a 48V Victron off-grid system for my camper van. Based on the manual, I need to do an initial charge on each battery before connect them in series.

Initial charge:

I used a Victron blue smart charger ip65 connect to a Victron 12/24v 65A battery protect. The charger red cable connects to IN port while the OUT port connect to Victron BMS 500 and then BMS 500 to the battery. Similar to this attached diagram but charger instead of DC load. (See the attached diagram)

I tried 4 attempts of charging. Each attempt of the charge is using adsorption 28.4v, floating and storage 27.0V, adsorption time fixed 24hours. As long as the charger jumped to floating stage, I will manually disconnect the charger, wait for all lights off then reconnect.

During each charge, from cell 1 to cell 7 will stay at 3.51v to 3.52v while cell 8 will stay at 3.48v all time. I do see BMS turned on and off all the time. I know this is normal, however BMS and charger cut the power and reduces the current to <1 amp or even 0 amp. Is this mean the balancing is not active since it is less than 1.8 amp? is this because my battery is full so it can’t flow any current anymore?

In conclusion, no matter how many times I tried, the last cell always stay at 3.48v while other cells are 3.51-3.52v. I can’t get the battery fully charged to 28.4v. The BMS saying the SOC is 100% but the battery voltage stop at 28.1V. Does it suppose to reach 28.4v max as fully charged?

I contacted the battery distributor and they told me maybe the battery is not rebalancing enough and ask me to charge more.

My question: is there anything I did wrong? Is the battery behavior normal? Do I need to discharge the battery to 50% and then charge again? Or I should keep charging while it’s 100% SOC to let it balance.

Please help.

 

[sunshine_eggo]

My question: is there anything I did wrong?

Yes. You thought you did something wrong.

Is the battery behavior normal?

Yes.

Do I need to discharge the battery to 50% and then charge again?

Never.

Or I should keep charging while it’s 100% SOC to let it balance.

No.

Please help.

Your prayers are answered...

I speak a lot of Victron, but I'll admit to knowing a lot of nothing about their BMS options, but general LFP battery knowledge applies.

3.48V @ 0A is definitely fully charged. 3.48-3.52 range is a non-concern. ALL brands arrive with some level of imbalance.

Point of interest: you absolutely, positively can get LFP fully charged as low as 13.6V with a very long absorption period.

The batteries are reaching 28.4V according to the charger:



There is always a small voltage drop between charger and battery.

What are your charge termination criteria??? Provide charger settings capture?

 

[AgentOneee]

Yes. You thought you did something wrong.



Yes.



Never.



No.



Your prayers are answered...

I speak a lot of Victron, but I'll admit to knowing a lot of nothing about their BMS options, but general LFP battery knowledge applies.

3.48V @ 0A is definitely fully charged. 3.48-3.52 range is a non-concern. ALL brands arrive with some level of imbalance.

Point of interest: you absolutely, positively can get LFP fully charged as low as 13.6V with a very long absorption period.

The batteries are reaching 28.4V according to the charger:

View attachment 271115

There is always a small voltage drop between charger and battery.

What are your charge termination criteria??? Provide charger settings capture?

Thank you so much for your reply. Here are my charger settings (see attached screenshots). I used the built-in Smart lithium (LiFePO4) charge profile from the Victron Blue Smart Charger but increased the adsorption time to 24 hours instead of 2 hours pre-set.

My VictronConnect app battery has never indicated fully charged. You can see “Last Full Charge” is “Unknown” and cell status is “imbalanced”. I worry if one of the cell defective from factory.

I unplugged the charger and let the battery connect to BMS and battery protect, after couple hours, the battery voltage dropped to 26.67v. Each cell is 3.33-3.34v. Why voltage dropped this fast without any load? Is this normal?

Based on manual, the battery is fully charged when the battery charger has reached to the float stage and the VictronConnect app battery cell status is “Balanced” (it said each cell should be 3.55v), but I never see that.

Could you please let me know how should I properly initial charge or fully charge my batteries before connect them in series? Should I ignore the VictronConnect app?

The last screenshot that contains “Battery Monitor Settings” is the BMS 500 settings, its default settings, I don’t know if I need to adjust so I leave it as it is.

 

[sunshine_eggo]

Thank you so much for your reply. Here are my charger settings (see attached screenshots). I used the built-in Smart lithium (LiFePO4) charge profile from the Victron Blue Smart Charger but increased the adsorption time to 24 hours instead of 2 hours pre-set.

Disable BatterySafe
Reduce absorption time to 2 hours.
Everything else looks fine.

My VictronConnect app battery has never indicated fully charged. You can see “Last Full Charge” is “Unknown” and cell status is “imbalanced”. I worry if one of the cell defective from factory.

I don't know the criteria the battery/BMS uses for these values, but based on the 3.48-3.52V range you provided, it's fully charged.

There is ZERO evidence of a defective cell.

I unplugged the charger and let the battery connect to BMS and battery protect, after couple hours, the battery voltage dropped to 26.67v. Each cell is 3.33-3.34v. Why voltage dropped this fast without any load? Is this normal?

Yes. These behave similarly to lead acid where you have to charge to a higher voltage, but they'll settle to a lower voltage when charge is removed.

Based on manual, the battery is fully charged when the battery charger has reached to the float stage and the VictronConnect app battery cell status is “Balanced” (it said each cell should be 3.55v), but I never see that.

And you may never see 28.4V at the battery, so it won't get there.

Every device that measures voltage has an associated error. Your charger is going to naturally read high because its voltage is influenced by the charge current. The battery is measuring it's own "open circuit" voltage, which is NOT directly influenced by the flow of current.

Could you please let me know how should I properly initial charge or fully charge my batteries before connect them in series? Should I ignore the VictronConnect app?

In my opinion, the battery is fully charged and balanced enough. If it's really important to you, raise absorption voltage incrementally by 0.1V at a time until you get the warm fuzzies you need.

The last screenshot that contains “Battery Monitor Settings” is the BMS 500 settings, its default settings, I don’t know if I need to adjust so I leave it as it is.

Looks fine.

 

[AgentOneee]

Thank you so much. Your information is priceless to me. Really appreciate!