Crossbow

Battery model is on the battery.  And in the data sheet for the FX2NC controller. Unplug one and plug in a new one.  You're already blank so no worry about losing the program.

SC09

Battery light is on, PLC is blank because the battery is dead.

If the machines are identical, you may be able to upload the program from one and download it to the other.  GX-Developer or GX-Works2 should be able to talk to that PLC.

CC-Link is a specific cable.  It's listed in the manuals.  As for the specs, I don't have them, haven't touched CC-Link in 8 years.

Ethernet should use CAT5 cable, which has 8 wires even though only 4 get used. CC-Link is a dedicated cable.

When receiving data from Rockwell, make your receive array 4 bytes larger.  AB adds 32 bits on outbound packets.  So if you set your AB to send 30 bytes, you need to set the CJ to receive 34 bytes or the packets wont be the same size and communication will fail.

Well in my 22 years of automation I have seen multiple instances where the program in an HMI uses a PLC register to say what screen number it should be on.  If the PLC isn't connected, or that value is set to an invalid choice, then it can't read that value and may not be displaying anything.  Have you tried pressing the top two corners to bring up the system menu?  If you can't access the system menu, you likely need to return it for repair.

One program of either ladder or structured text is a function block, but in Sysmac the ladder can be broken into multiple sections.  If you were writing scan programs, there is no limit to the number, but yes, a function block is made of one program.

Are you certain the program in the screen isn't waiting for the PLC to tell it what screen number to open?   The only thing that can write the internal card is the HMI itself.  You cannot access it, as you notice when you try to put it in the PC...

I'm with A.  One FB per module.  That way if a change has to be made, only one FB is affected. What do you mean by 'Omron doesn't support multiple ladder routines'?

FX3U-ENET-ADP connects on the left side of the PLC, and is basically a serial to Ethernet adapter.  It's primary use is programming over Ethernet. FX3U-ENET is used for controller networking and HMI connection.  FX3U-ENET-L is a lite version, it was not sold over here so can't tell you what the differences are.

As far as I know MDT isn't working with Studio.  My understanding is it has the ability to access the PLC directly, and is backing up from there.

Multiple projects make it more difficult to manage, and kinda defeats the purpose of an integrated environment...

There is no issue with the VM showing as COM1 when the real PC is COM2.  You are creating a virtual machine, and in that machine, the port you connected is the first one.  So it becomes COM1. Some USB serial adapters do not work well with PLCs, as they may not implement the entire serial command set or handshaking.  I had good luck with one from Keyspan (USA-19HS) for every PLC I ever tried.  Perhaps your cable needs to be different too.  Some devices require crossing the TX/RX wires, or making sure the handshaking wires are connected.  See if the vendor can provide a cable pinout.