Adding more batteries to AC300

I currently have an AC300 and 2 B300 batteries hooked up and it’s working well. I just ordered a third battery to add to the system. I know it’s very simple and plug & play, but could anyone show me how to properly hook up a third battery to the two I currently have on the AC300? Which port goes to which on the new battery I guess is my question.

According to all the AC300 images and the user guide booklet, the AC300 has two battery expansion ports, and each can manage two batteres in series (actuality there are in parallel). The B300 has two ports on its side to allow the chain to continue. So the correct form is to connect the first B300 to any of the AC300 expansion ports by plugging in with the P090A cable to both, then slide to cable lock forward. That has two functions, first to lock the release pushbutton out, and to signal the AC300 that a B300 is connected. Then the second B300 should be connected to the free AC300 expansion port. The third B300 can be connected to the first or the second B300 by using the second expansion port on the first or second B300 with its P090A cable. Then the last B300 can be connected to the remaining B300 by the same method. At the end you will have two chains of two B300 batteries on each AC300 expansion port.
In theory (which has not been tested) you can connect all four as one chain into one port of the AC300 and all four will be recognized and managed. Someone tried connecting a fifth B300 battery and the AC300 did not see it at all. The new AC500 can see six B300S.


@contem4 Connect the third B300 to one of the two previous B300s, and it will be fine.


I really want to have clarity on how to connect my 4 B300 to the AC300.

  1. All 4 B300 one after the other to one connection of the AC300
  2. 2 B300 to each of the two AC300 connections.
    Are there differences between the two connection variants in terms of how the system functions?
    The B300 also have 2 ports each. Does it matter how I connect the B300 to each other?
    I would be happy to receive binding information from Bluetti Service.

Thank you!

ich möchte wirklich Klarheit haben, wie ich meine 4 B300 an den AC300 anschließen soll.

  1. Alle 4 B300 nacheinander an einen Anschluss des AC300
  2. jeweils 2 B300 an jeden der beiden Anschlüsse des AC300.
    Gibt es bei der Funtion der Anlage Unterschiede zwischen den beiden Anschlussvarianten?
    Die B300 haben auch jeweils 2 Anschlüsse. Ist es egal, wie ich die B300 untereinander anschließe?
    Pber eine verbindliche Auskunft von Bluetti Service würde ich mich freuen.

Vielen Dank!

Das wäre wirklich interessant!

Different connection methods will have differences. It is recommended to connect one AC300 to two B300s in a symmetrical way. This type of connection can balance the State of Charge (SOC) between the batteries.

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Thank you, but that only partially answers my question.
It involves connecting four B300s.
and how these should then be connected to each other.
Normally it shouldn’t matter because I suspect that the batteries are connected in parallel in any case since the voltage (V) is the same no matter how many B300s are connected.
As a result, the SOC would normally have to align automatically. But they don’t do that, instead the BMS of the AC300 tries to control this by determining which B300 is currently being charged/discharged.
The SOC will certainly not recover exactly,
but calculated or, more or less, estimated from the load/consumption over time.
I have found that calibration only for a short period of time prevents the SOC values ​​of my 4 batteries from differing significantly, up to 4 times.

Why there are such large differences?
I have tried all variants of compounds between the AC300 and the 4 B300, but the SOC values ​​always differ after a while definitely.

What interests me is how the AC 300 behaves when a B300 is completely discharged…
Does the AC output then switch off or the remaining ones continue to be discharged.
If that’s the case, the different SOC wouldn’t be such a big problem
when all batteries are gradually charged back to 100% when reloaded…
Many reports about this difference in discharge have prevented me from purchasing an AC300 or AC500 with 3 or 4 batteries.
It seems that with only two batteries there are fewer problems.
Bluetti can certainly go into this in more detail and what the possible solutions look like…

The batteries are connected in parallel, so theoretically their voltages should be the same. However, slight voltage differences can lead to variations in discharge rates, resulting in different State of Charge (SOC) levels between them.

Have you performed any firmware upgrades related to this before? If not, please provide the SN code and BMS version to @BLUETTI_CARE. Please note (101416/102404/102107 have already been mass pushed).

Upgrade the firmware first and then perform charge-discharge cycles.

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Hello Marcus,
I have tested it. When one B300 goes to 1% it will not continue to discharge.
Only when all B300 are at 1% will the AC300 continue to discharge and then switch off.
Apart from this problem, my system works satisfactorily and can be recommended; especially since prices have fallen significantly recently.

Hallo Marcus,
ich habe es getestet. Wenn ein B300 auf 1% geht, wird er nicht weiter entladen.
Erst wenn alle B300 auf 1% sind, entlädt der AC300 weiter und schaltet dann ab.
Bis auf diese Problematik funktioniert meine Anlage zufriedenstellend, und man kann sie empfehlen; zumal die Preise in letzter Zeit deutlich gesunken sind.

Hello BLUETTI Admin,
my firmware is up to date.
I calibrated several times but the problem
was not eliminated by this.
BLUETTI may be able to provide me with an update tailored to the problem.

Thank you!

Hello BLUETTI Admin,
meine Firmware ist auf dem neuesten Stand.
Ich habe mehrmals kalibriert, aber das Problem
wurde dadurch nicht beseitigt.
Eventuell kann BLUETTI ein an das Problem angepasstes Update für mich zur Verfügung stellen.

Vielen Dank!

Hello Akel,

that is interesting. I have spoken to a few users where the AC output switches off when only one battery is completely discharged and the remaining ones still have capacity.
If, as in your case, the battery can continue to be discharged until the last battery is empty, the different charging states shouldn’t actually be a problem. Or am I wrong?
As long as all batteries are 100% fully charged again, it doesn’t matter how they are discharged as long as the full capacity is available.

Greetings Marcus

Can confirm. When one of the B300 is empty, the AC300 shuts off. I have two B300 connected to my AC300 and on of them still have one lamp on while the other is completly empty.

Also can confirm different fast charge and discharge. My B300 have a ~15% difference.

If there is any “custom” Update, that would be great!


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Hello Erik,
yes, that’s what many users told me. This means that the AC300 and AC500 are not really usable with more than one battery, as it is impossible to estimate how long the remaining running time will be if one of the batteries is discharged before the other.
I think this is a problem that cannot be easily solved with a software update. There have been reports of this on the internet and in forums since the devices came onto the market.
Many users seem to only operate the AC300 with one battery, so that’s of course not a problem.
The AC300 is advertised with an extension of up to 4 batteries. And that’s not really possible…
What is Bluetti currently doing to solve these problems, or is there perhaps no way to solve the problem with the current devices?
I’m sure Bluetti will inform us here in this post.

Greetings Marcus

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I tried it again yesterday to be sure that it was actually the case.
It was a good time because I wanted to recalibrate the batteries anyway.
#1 10%
#2 7%
#3 23%
#4 6%

I used a heater and discharged 1500W via the AC output.
Only when all batteries had 1% did the discharging continue and the AC300 then switched off.
Logically, 0% never appears before switching off.
I can’t explain why it doesn’t work that way for you.
Hopefully BLUETTI will comment on the problem here.
ich habe es gestern nochmal ausprobiert um sicher zu sein, daß es tatsächlich so ist.
Es war ein günstiger Zeitpunkt, denn ich wollte die Akkus sowieso neu kalibrieren.
#1 10%
#2 7%
#3 23%
#4 6%

Ich habe mit einem Heizgerät und 1500W über den Ausgang AC entladen.
Erst als alle Akkus 1% hatte und ging das Entladen weiter, und der AC300 schaltete dann ab.
Logischerweise erscheinent niemals 0% vor dem Abschalten.
Ich kann mir nicht erklären, warum das bei euch nicht so funktioniert.
Hoffentlich äußert sich BLUETTI hier noch zu dem Problem .

@Akel Could you please provide me with the SN, firmware of your AC300, also, the BMS version of the 4 battery packs? I will check with the technician to do a scene recurrence and get back to you ASAP.

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Here is the Spezification.

Thank You!

@Akel There are two points I need to confirm with you:

  1. Does the same battery pack reach 1% first every time?
  2. Since one battery pack reaches 1% first and the AC300 has stopped discharging, how can other battery packs also reach 1% and then continue to discharge?

Es gibt zwei Punkte, die ich mit Ihnen bestätigen muss:

  1. Erreicht derselbe Akku jedes Mal zuerst 1 %?
  2. Da ein Akku zuerst 1 % erreicht und der AC300 nicht mehr entlädt, wie können dann auch andere Akkus 1 % erreichen und sich dann weiter entladen?

I have to test it intensively again.
I have now connected the batteries differently and used both outputs of the AC300.
I’ll get in touch in the next few days.

Greetings Joachim
ich muß das erst nochmal intensiv testen.
Habe die Akkus jetzt anders verbunden und beide Ausgänge des AC300 verwendet.
Ich melde mich in den nächsten Tagen.

Gruß Joachim

I have tested the charging/discharging behavior of my AC300 and 4xB300 again.
Two B300s are connected in series to each of the AC300 outputs.
The deviation is sometimes up to 40%.
I have calibrated the system several times.
The B300 numbers 1 and 3 as well as 2 and 4 are each on one string.