Dc lo keeps blinking on the fridge and lights go low in rv, power converter middle light is blinking green
The battery is not being charged OR is no longer accepting a charge.
The inverter does not charge the battery. An inverter consists of components that first convert the battery's low (12) volt "direct current" (DC) power used to power automotive devices to a higher (120) volt "alternating current" (AC) power that is required by nearly all household appliances to operate properly.
The charging of the battery occurs when either the RV's engine is running and spins the alternator, etc. OR when connected to another charging device - whether it is permanent or portable.
With the RV engine running, there should be about 13.5 - 15 volts, DC on the battery posts or terminals. This voltage is coming fromt he RV alternator and since it is greater than the 12 volt battery, "charges" the battery. If you use a portable charger - that is part of a generator, or plugs into a power port at a camp site, etc. this will charge the battery.
When none of these things is happening, the battery voltage will slowly drop. Once it is at ~10 volts, it is "dead" and will need to be recharged.
The battery will no longer accept a charge if a "cell" inside it has "opened" or "shorted", or if the battery is at the end of its useful life. The battery state can be checked quickly by any mechanic.
I hope this helps & good luck!