The LG MonoX ACe 300W Module has been discontinued (possibly reason for price reduction?). It has been replaced by LG Mono X ACe 300W PerfectAC Module. I'm guessing the original wasn't just "perfect" enough? ;)
Can micro-inverters be used in ac-coupled systems?
For dc-coupled systems, are there battery charge controllers that accept 240v ac has input source?
They are always improving on technology. I wonder what comes after perfect next year. They probably work fine together.
Any grid-tied (interactive) inverter will work in an ac coupled system. The interactive inverter will not know the difference from the real grid and the ac coupled grid made by the battery inverter.
In order to control overcharge from the interactive inverter, the battery inverter can make the inverter turn off by slightly changing the frequency and making the interactive inverter anti-island (turn off).
There are other ways of controlling charge, such as when you have products that were designed to go together they can communicate.
Another way of controlling charge is a diversion load, which will turn on when the battery is charged and there is extra sunlight. A common diversion load is a heating element in a hot water heater. The NEC does not allow us to rely upon the diversion load, so we will need another way to control the overcharge.