I have used the Vertamax 3000W inverter on and off over the past two months with various types and configurations of solar panels and batteries. It performs well under a load of up to 1200W and probably performs well beyond that, although I have not tried. It is well built.
One thing that I have noticed is that, as stated in the description, it does shut off under low voltage. However, the shutoff voltage is around 11.8V or 11.9V – not the 10.5V (+/- 3V) shown in the instruction manual. Of course, this is good for a lead acid battery under load because the inverter will shut down before the battery completely runs down. Running the battery completely down will dramatically shorten its life.
The description/manual also states that “When the input voltage rises to approximately 11.4 – 11.9V DC, the inverter restores to normal operation and the red FAULT indicator will turn off.” This is not correct. Even after a battery is fully charged to 12.9V, the fault like still blinks and the inverter does not come back on. I called WindyNation and spoke with a knowledgeable gentleman who verified that the only way to get the inverter to resume normal operation is to manually toggle the ON/OFF switch. This means that, at a remote unmanned site, a low voltage condition will cause the power to be off until someone can visit and reset it.
WindyNation told me a good rule of thumb to minimize the likelihood of batteries being run down below 50% – which is about as low as it is safe to go without damaging lead acid batteries. The rule of thumb is that choose a bank of deep cycle batteries that have as many amp hours as your solar panels have wattage. For example, six 100 watt solar panels should have a battery system rated at 600AH. This is general guidance and the exact ratio depends on the amount of sunshine in your location and the season. But, my experience over the past few months in North Texas is pretty much in line with this recommendation.