I upgraded both the battery and screen firmware to the latest versions and saw no change.

I made sure the inverter was on the latest firmware version.

I upgraded the wifi dongle to the latest model, which was the first time that one battery was displayed, the master battery, but never all 3.

I then went down the rabbit hole of changing out every cable multiple times, cycling the dip switches to make sure they were in the proper position, reinstalling the firmware, and after this, I never saw more than one battery most of the time. There was a moment when I saw the master and one other battery, and it was battery 0 and 1 or battery 0 and 2...which was also very odd.  I will note that if anyone was curious, the cables can be any normal Ethernet cable. I use CAT 6a because I have a lot lying around from my network.  For a long time, I was sure it was a cable issue or a port issue.

This is the change that brought up all 3 batteries!. I changed the master battery from the one I had been using and the oldest battery to the second battery I had purchased.  This just required isolating all the batteries, both breaker and BMS switches, and then changing the dip switches...  voilà, all of a sudden all 3 batteries are working and have been for a couple of days.

I have no idea why this one change made a difference unless there is a failed component in the original master battery.  Possibly one of the com ports or the 485 port has a damaged connection, I don't know, but it is working.

This was important because I want to track the cycle count more than any other data point.  My cycle count is 495, 323, and 14, so it will be interesting to see how cycles impact capacity. I cycle my batteries every day from 100% to 20%.  It's the mild time in Arizona, so I don't go below 45% right now, but in a month or so, I will deplete all batteries down to 20% and go on grid power before midnight once the AC starts running 24/7.  This is the first summer with 3 batteries, so it will be interesting.  My only goal was to get through the utility extortion period of 4 pm to 7 pm where they charge a solar tax to really screw everyone that does not have batteries.  That one charge can easily double my power costs.

Firmware is updated on 3 batteries to Z02T17

The dip switches are in their proper order per the manual's pictures

CAN protocol is set to EG4/LUX, and the inverter's Lithium brand setting is configured to 1

Under configuration/devices, I show 3 batteries, but I will say that any changes to the configuration takes the monitoring software quite a while to pick it up, long lag, but eventually, it does show all 3 batteries, and that is the only place it shows it.  The phone app also only shows 2 batteries no matter what configuration the system is in

A new dongle was installed, which did work partly, and I now see 2 of the 3 batteries.  I replaced all ethernet cables with known "good" ones, but still, only 2 batteries are shown.  I thought maybe the order of the ethernet jumpers between battery RJ45 ports was important, so I have adjusted every conceivable position without effect.  

Are the 2 RJ45 ethernet ports on each battery in some kind of series/parallel loop? and does it matter how each battery is jumpered between them, cause that is all I have left.  What is even more odd, I always have just 2 batteries shown, and I always have the master battery shown, but in one RJ45 configuration, I get master and battery 2, and in another configuration, I get master and battery 3, so the hardware appears to be working.

The manual shows a picture where the ethernet cables go from the 2 RJ45 ports on the master battery to each secondary battery, so I did that, and I got the master and battery 3.  I then tried jumpering from one master RJ45 port to battery 2 and from battery 2's RJ45 port to battery 3's RJ45 port, and I then get only the master and battery 2 shown.  At no time do I ever get all 3 batteries?

I believe we experimentally determined the battery comms were only CAN protocol. At one point we purposely set the battery RS485 protocols to unworkable settings in the BMS and the inverter still communicated fine.

I think we found the RS485 battery firmware instructions buried (pdf file) in the .zip file download with the tool and firmware files. It's been a while, so the details escape me. The firmware download file had two parts, RS485 and RS232. The RS485 software tool worked well with the cable/dongle from Signature Solar. We never could understand or perform the part 2 (RS232) update. 

These types of experiences with the brand caused us to step back from more sites using them. Too many undocumented 'secrets'. We are watching and hoping the company can mature-there is an important opportunity for them.

Good luck!

All dongles, except those starting with BA, can report detailed battery information. It also depends on which battery model you have. The LifePower4 V1 model cannot communicate detailed information to the inverter.