i think you need more batteries
what is the age ,size , type etc.. of the two batteries you now have
try this test
shore power plugged in
your new ats disconnected or turned off
fridge connected to use inverter power not shore power
test with inverter on in use and
converter charging batteries, to be the extra batteries you do not have
if it works, inverter is ok but not enough battery
if it doesn't work, inverter is not strong enough
(if it exists) the inverter surge problem is time related..
it doesnt hold tne surge rating for a long enough 'time period'
it holds for milliseconds, when it needs to hold for 'Seconds' 5~10 IS ENOUGH
my pv1250 will hold 2500 for 10seconds
and 1875 watts for many minutes
it will power my 1100watt MW, that draw 1650w
and bake a potato
i prefer using the generator for this to save battery.. but it has come in handy late at night
