If you continue to discharge those batteries, at the very least you'll be looking at new batteries. Get the charger and put it on to keep the batteries charged. If you didn't bring your meter, go buy another one. At this point, you're guessing and so are we.
You still haven't answered some simple questions put to you, so I'm guessing you really don't want any help....
What type, model etc inverter/converter do you have.?
What brand batteries? 6V or 12 and how old.?
Check the cabling to the batteries and at the inverter/converter.
Provide as much info as possible to get the best possible answers....Dennis