"Must be my Inverter which takes DC from batteries & inverts it to AC"
Yes. Probably.
"How come I can get AC from my batteries but no DC????"
Is the Battery Enable/Disable switch "enabled"? If not, typically no DC to coach 12V outlets or equipment.
You've given no info about what you're driving/pulling.
Year/Make/Model might help others troubleshoot your questions.
My comments are just guesses based on general AC/DC functionality.
Mike. Comments are anecdotal or personal opinions, and worth what you paid for them.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)