Bluetti techs or anyone, I have an AC500 and six B300S (Indiegogo campaign) which I first set up in March '23 according to a diagram (showing two serial stacks of three B300S) in user manual and experienced no functional problems. Today, June 22, I took apart the entire system and moved it to another location in the same room, taking care to replicate the previously functional cabling/connections. Now, all six B300S are recognized by the head unit, but only B300S #6 (at the top of one of the stacks) is reported by the head unit to be online (green dot) and usable/chargeable both with AC and PV. SOC is 90+% on all six B300S. On the app battery report, B300S #1-#5 show a gray struck-through symbol beside the term “battery parallel,” which I assume is equivalent to the non-green (is it maybe yellow?) dot appearing beside “battery online” for B300S #1-#5 on the head unit. App shows battery #6 with a blue symbol at “battery parallel.” I have updated firmware, reset to factory, removed and reseated all cabling multiple times and in various combinations. There are no error codes. It seems impossible that there is a sudden fault in the equipment. I think there must be a setting that changed, or maybe a cable isn’t seated. Long-winded in an attempt to be thorough, sorry. Very frustrating. Anyone have any ideas? Thanks.
Interesting problem. I’m not sure what the answer is but did you also use the exact same battery in the exact same place in the stack? the reason I ask is that when I first set up my AC200Max with an additional battery it came up as battery #3 rather than #2, I saw on this forum somewhere that the very first time you plug in a battery it is designated by the port that you plugged in to and the firmware will always see that battery as what it was first designated as.
Great idea, doebut I did exactly replicate every aspect of the previously functioning installation, so nothing should have changed. I fibbed a little when I said the firmware was updated. I updated the head unit firmware but did not update each individual B300S because it was not practical to do at that point and it made no sense as a possible cause of the problem. Leaving no stone unturned, I am now going to break apart the 500+ lb system (whew!) and update the firmware on each B300S individually (as specified by Bluetti) and at the same time determine if each B300S is individually recognized and activated to online status by the head unit. If that goes well, which I expect, I am then going to reconnect all the B300S units in sequence and see if the head unit accepts them. Maybe there’s a newly developed defect (or more than one) in the six 150A cables and 12 connectors. Surely this undesirable, unexpected, and relatively elaborate finagling of the system components will yield some useful info and positive results. 
I will report my findings back to the community. Thanks to you and any other members who want to join in the fun. WAW
First, doecliff. I’m sorry about the typo (omitted comma, should have been “doe, but”) in my reply to your helpful response (the only reply). Anyway, I played around with the battery cables and found out the cause of the “battery offline” issue. It turns out that the locking slide lever on the connector plug also actuates the microswitch to complete the connection. I had previously read somewhere that it was only necessary to completely seat the plug to actuate the microswitch, with no mention at all of the locking lever. This advice was wrong, or maybe I misunderstood it. Because I wasn’t consistently setting what I thought was a simple locking lever in my haste to complete/test the hookups, the battery offline errors were all my mine. Never have had this problem with my AC300 or AC200 MAX, I might add. Lesson learned.
Excellent! glad to hear it was resolved.
Thank you for the follow up on the locking slide lever needing to be slid to lock to actuate the cable. Who know - now I know. Thanks!