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I’d likely only run the microwave for 2-3 minutes... I’d run two 225ah lithium batteries. [quote]
are these 6v batteries? if so, and in parallel, they'll then be the 12v the Inverter needs, but also now 1/2 the stated ah of the batteries - so 112.5 ah for the battery bank.... and, since the typical understanding is that 50% of the battery bank power is what you should try not to go 'lower' than, you will have around 60ah of usable battery power, roughly speaking.
if they are 12v batteries, then you'll have about 120ah...though 12v batteries aren't the typical 'deep cycle' that the Inverter can make best use of