Odds are the inverter is good the batteries are a bit low.
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IF the inverter is "Fried" odds are good it's the "T" fuse inside the inverter
And that for that inverter might be as much as sixty dollars but likely less.
And user replacable I might add.
the fuse. if blown is a flat copper bar with a big "barrel" around the middle of it 1-3 inches long two bolt holes (one in each end of the bar)
The LINK is **NOT** the fuse you need but the design is the same (Too small a fuse)
Click here to see a 100 Amp version you likely need 250 or 300 amps