you don't say if the red led is on the inverter or the control panel. Regardless, it is most likely that your batteries are below 10.5 volts.
I would use a car charger to try and charge the batteries. One of the automatic one you can find at Walmart works great.
It might be that if you get the batteries charged up the inverter/charger will start working again. This happens in my coach when I set up or teardown with the air conditioners on and it is hot. I believe it is a sign that my batteries are old and/or my inverter is not getting enough cooling air.