estimating battery discharge current approximately from ac load current
A good first approximation would be to:


Calculate the apparent power in VA.  That's easy, just take the RMS voltage times the RMS current, in your case 10A * 230V.
Divide that power by the battery voltage to get the battery current.  Note that this assumes a perfect converter, which doesn't exist; remember, this is a first approximation.
According to your question, you're done, but you may also be interested in maximum runtime.  For that, divide the battery's capacity (150 amp-hours in your case) by the current that you got in step #2.


Okay, now that you have an unacheivable maximum performance figure, you can start accounting for inefficiencies, specifically:


The converter isn't 100% efficient.  Perhaps more like 80-90%.  The other 10-20% represents extra current pulled from the battery and converted to heat.
Battery capacity is not constant with load.  It tends to decrease under heavy loads so that you may get 170-200 AH under a light load and closer to 100 AH under a heavy load.  Exactly how much it changes depends on the specific battery.