AC300 - Different BMS on B300 and different discharging rates

Hello together,
I bought an AC300 + 1 B300 3 months ago. Now I added another B300.
The first on has a BMS Version 1021,06 and the second one a BMS Version 1014,16.
Before I connected the two B300 to the AC300 I made sure they had the same load, 70%.
But thru the discharging process the B300 v1021,06 is discharging much faster than the B300 v1014,16.
I started at 70% to 70% and now the ratio is 29% to 50%. I have connected the batteries parallel.

  1. Is this normal procedure or not?
  2. If it is not normal procedure, what do I need to do? BMS firmware update and calibration?
  3. Is the BMS firmware update on AC300 save? Because I saw there were quite big problems on AC200.

My versions on AC300:
IOT 9014,10
ARM 4037,05
DSP 4036,02

Thanks a lot for your help!

I have the same problem on my AC300 +2 B300 batteries combo. I’ve been going back and forth with Bluetti tech support for about three months. I just want to know why the AC300 allows for such an imbalance. If I figure something out or hear something that makes sense, I’ll let you know.

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Thank you very much for your response and your support if you hear about a solution!
I hope we get an answer from Bluetti admin on this issue.

I wonder how common an issue this is? It seems as though more people would run into this issue IF they are using their unit 24/7 or continuously. Which leads me to believe that a lot of people buy it and it sits for a few months, then they use it for an hour or so, charge it up and it sits again. It seems as though a common theme is that the batteries have a different BMS version. I would think that Bluetti would look into the issue seeing as though when these AC300 +B300 batteries go into full time use, they’ll have a flood of issues (fix the problem now, then when they are flooded with upset customers they can give them a quick solution).
IF it were a calibration issue, calibrating the battery would fix it. I have done three or more calibration cycles in the last three months. Perhaps the issue is that the battery cannot be calibrated. Wouldn’t this point to a defect or failure in the BMS? If that’s the case, you would think that Bluetti would be VERY interested as we are discovering an issue that should have been resolved in a beta test. All the advise I have received from Bluetti indicates that the batteries need to be calibrated. But calibration doesn’t fix the issue. This tells me that either calibration is not the issue or that one of the batteries will not calibrate (B300 issue or AC300 issue). So maybe Bluetti is as dumb founded as we are? Either way, it seems like it would be in Bluetti’s best interest to get to the bottom of this, whether it be a glitch (software related) or defect (hardware related).

@Giuseppe May I ask your two B300s are connected to the AC300? Or one by one in series? If it is connected in series, please connect both B300s to AC300.
In addition, about 10% inaccuracy is normal, the discharge rate is dynamically adjusted, and the final battery is discharged to zero simultaneously.

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Hello BLUETTI Admin,
both B300 are connected directly to the AC300. One to the port BAT 01 and the other one to BAT 02. Right now I have 21% difference between the two B300. How shall I continue?

Please answer also those 2 questions?
Is it necessary to update the BMS versions so that both B300 have the same BMS version?
Is the BMS firmware update save so that I do not run into more difficult problems?
Thanks a lot for your support!

I continued discharging process. The AC300 kept a inaccuracy of 20% instead of 10% until the ratio of 40% Batterypack1 to 20% Batterypack2. Then the difference got less and less until 5% where both batteries discharged simultaneously.
I had set the Battery SOC Low to 20%. In the display it says: “Battery SOC low: When battery is drained to this value AC300 will automatically cut off power output.” But the AC300 continued power output and drained the batteries to zero. Why did the AC300 not cut off power output at 20% ???
Now I am charging the batteries with AC supply at 8A and the inaccuracy between the 2 batteries is about 2 - 5%.
Is it recommended to update the BMS versions so that both B300 have the same BMS version?
Is the BMS firmware update save so that I do not run into more difficult problems?
Thanks a lot for your support!

The inaccuracy during charging reached a minimum at about 45% (45 to 44) and reached a maximum on the upper end 87% to 65% between Batterypack1 and Batterypack2. But at the end both levelled out at 100%.

Do you primarily charge via PV/solar? I do and I am wondering if the battery imbalance is made worse when PV/solar is the primary means of charging the batteries.

No so far I charge only via AC adapter. I need to find time to investigate into PV.

@Giuseppe These two BMS versions are the same only the chip manufacturers are different.
According to your description, these two battery packs can be filled and discharged together, and the machine will not cut off the output.


Good evening, if you remember I had the same problem as you.
My system is 75% powered by the solar panel and has a 25% power reserve.
I have 3 B300 batteries, 1 with a different firmware to the other 2. I can confirm that after 3.5 months they have stabilised and have no more than 2 % difference when discharging and no more than 10 % when charging. I have a 2,150 kWh photovoltaic system which is oriented according to the seasons, and for 2 weeks I have already touched the production of 10 kWh per day. Right now I am in backup and tomorrow the solar production will start again and I will not have taken anything from the grid, so I am self-sufficient. The test was successful and fortunately my calculations were correct. If I can’t get all the power produced by March, I will buy the last battery pack for a total of 4 B300.
All this explanation to say that I am using the Bluetti AC300 + 3 B300 as my main source finally successfully. More if they finally update the BMS firmware I will let you know.
Have a good evening.

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I was told the same by Bluetti (that eventually the 2 batteries would balance). I wonder how long that takes? I’ve noticed no improvement and it’s been over three months. I suppose I’ll keep an eye on it and see how it pans out. I charge exclusively via PV.

Thanks a lot to everybodies contribution!
Especially also to BLUETTI admin

One more note. I did receive an email from Bluetti tech support which stated “Our R&D tells me that there is no new software to match this right now” in reference to the battery imbalance issue.

On another note, I was reading another post on the forum (AC300 no longer works - #20 by MontAnna) where some users were having problems with over-drained b300 batteries. I would suggest keeping a close eye on the b300 batteries. I wonder if the battery imbalance issue could have lead to a dead battery issue. Just FYI.

Had the same issue after adding an additional 3rd b300. After 2 calibration cycles (draining completely to 0% then fully charging to 100%), the difference is less and for my requirements good enough, but some difference is still there.

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Thanks for your response. May I ask how much difference you have still after 2 calibrations?

Sure, I see approx. 3-5% difference. I would not be surprised if that correlates with production tolerance of battery capacity.