AC500 SOC control not working after all Firmware and Software Updates

I have been emailing Bluetti.EU regarding the ongoing SOC issues with my AC500.
Minimum SOC is not managed by the system and maximum SOC is managed on an average across the 2 B300s, though I have seen Max SOC exceeded on occasion.
This average management allows for too wide a balance between batteries, upto 18% so far.

If I charge to 100% there is only 3-5% variance at the end of the discharge cycle to 20% SOC.
This is held to no more than 6% after 2 weeks or so.
When changing to 90%, as recommended, the initial charge can see 12-14% variance at 90%, which increases to 17-18% during discharge and leads to a 0% power off after only a few days.
The system requires constant observation as there is no day to day consistency in performance.

ie SOC set to 100% charge=Batt1 100%, Batt2 100% discharging to Batt1 37%, Batt2 33%
ie SOC set to 15%*-90% charge=Batt1 97%, Batt2 83% discharging to Batt1 35%, Batt2 17%

*I set the min SOC to 15% but in a normal daily cycle the SOC does not drop below 20% when batteries maintain a good balance.

Bluetti have not yet cured the issue, the latest response from them was that 10% variance is usual and that the balance will improve over time. I am not seeing any improvement, so why am I experiencing such an unacceptable disparity between the two batteries?

Is anyone else experiencing this large variation between batteries? And are your SOC limits being properly managed by the system?

I have carried out all the firmware and other software updates currently available.
I have reset the BMS with a battery drain and T500 charge cycle.

I need to set the SOC charge limit to 100% every few days to try to maintain an acceptable balance, but I am concerned that this will damage the batteries in double quick time.

It would be good to know if anyone else is having similar issues, thanks.

And Bluetti… it would be good to get some technical input from you.
Tina in Sales DE has lots of evidence of my issues and she will be receiving my latest evidence shortly, thank you.


I have an ac500 and it works well but has similar quirks.

The ups settings and ups power usage seem strange. It seems that even having my ac500 grid connected or ac charging plugged in for the ups to switch to is using about 150w or 200w ?

So with the same items plugged in it loses 10% per hour if i leave ac plugged in and ups set to pv priority 10% If I turn off the mains power leaving everything the same it loses only 2% per hour.

This is testing over and over for hours on end.

How can ups standby take so much power?

Also sometimes the ups doesnt even kick in at 10% and the ac500 turns off

I wish i could leave the mains power on to heat the battery since ive seen the temp go down to 5c before but i’m not sure how to prevent it draining the battery with ups on standy

I would just forget any ups function and have battery heating available.

Is it possible in custom settings to use the timer to just set all times zones to discharge? So there is no stanby ups to drain the battery?

Based on this issue, I have given feedback to the technical team. I will let you know once there is an update

@MarkP87 When multiple B300S and AC500 are connected, the battery voltage will become the same.
But the individual battery pack will have a difference in calculating soc, which leads to different soc values. soc can not indicate a good or bad battery, and the battery life is mainly related to the battery voltage.

Thank you for the reply, any incite into the inner workings of this system is appreciated, but here is my problem;

When charging to 100% SOC the system maintains a well balanced 4-6% variance between Bats 1/2 on discharge.

When I carried out the BMS reset procedure the 2 batteries reached full charge within 10 mins of each other, which suggests very similar charging rates and voltages in each battery.

However, as soon as I use a 90% Max SOC the variance is immediately 16-18% apart on first charge cycle.

When I initially charged 100% I saw an average discharge to between 25-35% after 16hrs.
Now charging on 90% SOC Max with 18% variance, I am having to reconnect to AC in as little as 12hrs and have had 2 drops to zero in only 13hrs with me employing extreme conservative usage. There is a definite issue here and we need to understand what it is.

So, a couple of logical conclusions/questions on my part that you can clarify/correct if you can please;

As the 2 batteries are run on 2 separate cable ports and(based on the T500 charge parity) the voltage in either battery is very similar, how is it possible in a 230v, 6amp AC charge over 4-5hrs that the SOC can perceive that there is 18% difference at 90%SOC…Unless the actual charge being received by each battery is different, ie the head unit is not distributing correctly. Is this just my unit?

Or 2, If the head unit is distributing correctly ,then the battery that is SOC18% lower must surely indicate a problem with how that battery is processing its charge.

My logical conclusion;
Based on the T500 charge I believe the batteries are pretty well aligned and I don’t believe the issue lies there.
Bearing in mind the other SOC control issue that the AC500 has, ie not responding to min SOC settings(like the AC300), I would put money on the the Firmware/Hardware in the Head unit not being able to properly manage multiple battery arrays, or my head unit has an issue?

I have hundreds of screen shots confirming my observations if they are of any use to the technical department.

Sorry to take your time, but I have invested half of my life savings into your product to protect our home from power cuts and reduce costs by switching to a new tariff, so it needs to work as advertised. That is all I am asking for.
Regards Mark P

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@MarkP87 Because of the difference in charge/discharge curve of each B300S, it causes each B300S to calculate its own SOC differently, and the host just accepts the SOC information uploaded by the battery pack. This causes the difference of SOC. When AC500 sets the SOC to stop charging, this SOC will be the average of each battery pack.
If you connect two battery packs, it is recommended to refer to the following diagram for connection.

I have been complaining about this since it first arrived after the campaign. What is specially annoying is, it gets out of level the more time passes. What seems to happen is the following: Charging state falls on multiple batteries over time. Once a threshold of combined charging is passed, only one battery is recharged until the combined state is below the threshold. Then everything starts from the beginning.
So if you start with two batteries at 80% SoC each and define a 80% SoC to hold, you will end up with one battery at 60% and one at 100% where it hurts the battery health in long term. This effect is also happening with 3 batteries. They promised to resolve the problem, but I guess I might have to sue for warranty and will end telling everybody how shitty Bluetti takes care of its products. Well, you decide…

This is BS you don’t even understand the problem. The SoC gets out of level because of something that is a well understood problem of your software. SoC level measuring works fine. Your software is just crap because it just charges one battery up to where it has 100% SoC and the other having 60% SoC because, well this gives an average SoC of 80%. Still one battery will get damaged being charged to 100% forever!

This has nothing to do with the charging curves of LiFePo. The problem has been described in detail and at this point I have to assume you either don’t want to understand or you can’t understand because you have some kind of mental deficiency.