I have several AC180’s which all get used in constant UPS mode with grid power connected.
I have noticed that when I connect either B80 or B230 Expansion Batteries to them to increase the AC180’s storage capacities, the following occurs.
Unfortunately the AC180 when it charges the internal battery from 99% back to 100% at least once every hour, not only draws power from the grid to do so but from the external batteries as well, which of course defeats the purpose of having them connected to increase the capacity if required when grid power goes off as they are constantly getting depleted.
The only way presently to work around this is to have the external power bricks connected to the appropriate batteries, but not something that is good for the batteries long term.
So my question is to Bluetti, can you now look at changing the software so that when the AC180 is connected to grid power it only uses that power source to charge its internal battery?
Or better yet maybe stop the AC180 from constantly depleting its internal battery capacity from 100% down to 99% then having to charge it back again to 100% when constantly being connected to the grid running in UPS mode?
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Utility and power bank mode will charge ac180 at the same time.
If there is utility input, do not use the battery pack, and then use power bank mode to replenish the power if there is no utility power -
AC180 will stop charging after charging to 100%, and will automatically charge when it falls to a certain level to prevent continuous charging.
Completely understand your response however I don’t think you understand what the problem is.
The entire idea of expansion batteries is to have a greater capacity when required, that would be when there is a failure in grid power.
Remember Bluetti sell the AC180 & AC60 as UPS’s so it is obvious that people would be wanting to have the largest amount of reserve capacity if required.
To do what you say I would have to be at the location of the AC180 when the grid fails to then connect the expansion battery, the idea is to increase the capacity of the AC180 using an expansion battery so that when I am not around the AC180 can power whatever is connected to it for longer.
Can you confirm if there would be any detrimental damage or wear on the expansion batteries if they were connected to the AC180 and to ensure they stay fully charged to a separate power bank which would top up the power level of the expansion battery once the AC180 drains it constantly?
This is the only way that I can see that I can increase the system capacity.
3 days and no follow up response, come on Bluetti please answer my concerns.
A further 3 days have gone by and sadly still no response from Bluetti regarding my recent clarification sort.
Have emailed tech support here in Australia direct so hopefully they will get an answer from tech support.
One can only assume they don’t want to answer the question here saying that it is detrimental to a batteries health to have a charger permanently connected topping it up, but this is exactly what both the AC180 & AC60 do internally, just worth mentioning!
Don’t have an AC180, do have an AC200MAX, but from reading about the AC180; yes one can connect an expansion battery, but the expansion battery operates to charge the internal battery of the AC180 power station 
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Could be wrong, but with the expansion battery connected to the AC180, if one charges the AC180, the expansion battery does not get charged. Hence, the expansion battery operates as a charger to the AC180 , and does not really expand the battery capacity as it does on other power stations like the AC200MAX . When you charge the AC200MAX it also charges the expansion batteries .
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Perhaps that is why you have observed that behavior, the expansion battery is charging the AC180 at the same time as the 120 AC pass thru charging 
. And probably why Bluetti gave that reply, though a bit pitiful in content .
Thanks and yes I am well aware of the differences in the AC180 & AC200Max as I have that as well with additional batteries connected which as you pointed out charge and discharge as required and are controlled by the AC200Max BMS.
What I am asking about is increasing the capacity of the AC180 and ensuring the B80 or B230 External Batteries can be left on charge 24/7 ensuring that remain fully charged if required to extend the usage time of the AC180 once the grid power goes down.
Remembering these AC180’s are used connected to the grid and as UPS’s, but still draw off the external batteries if connected to stay charged!
I have just had it confirmed by Bluetti Australia that it is not going to be detrimental to the B80 Expansion Battery, or for that matter any Expansion Battery leaving them connected to a power bank (brick) as the batteries will control charging and stop any overcharging.
So for me that means I can use them to expand the storage capacity of the AC180’s being used in UPS mode, ensuring that they, like the AC180 will always be at full capacity if required when the grid power fails.