Lap tops ?

Kiowan:
Sorry, totally forgot about this, when your engine is running the system voltage is around 14.3 or similar and there is more current available due to the batteries and the alternator producing power. With the engine off your battery voltage is going to be 12.5-13v and the only current you can draw is coming straight from the batteries. This is why when fully loaded your inverter is struggling.

I encounter similar issues if using high power equipment, I tend not to use my microwave with anything else running and if I use my vacuum then i’ll make sure the engine is running as it has a noticeable effect on how the vacuum runs. Basically if the inverter is struggling with the engine off then you’re loading too much on it at once and it’s having a hard time pulling all that power from the batteries alone, won’t necessarily damage it though unless its overheating and the protection circuit shuts it down. I’d also point out that my inverter is 2000 or 2500w, can’t remember which and those appliances barely break 1300w but pulling that from batteries alone is a task.

Thank you, very helpful, how stupid am I ? LOL.