85 watts is the regular charger's wattage.
I think that's only the output. There can be substantial loss from the input because of the conversion.
My 60W power adapter says output is 16.5V at 3.65A, which is 60.336W. However, the input says 1.5A at 100-240V. At minimum that's 150W (at 100V) although I'm pretty sure that it's a peak value. It obviously doesn't say how it scales with a typical 110-120V source like an inverter.
For the OP, what does it say on the power adapter for the input current? I'm thinking that you probably want at least 200W. Most inverters are rated for a specific steady output and a higher peak output.