Calcium Premium refers to the chemistry of the electrodes in the battery. Rather than pure lead they will use a lead-calcium alloy to produce a battery which has lower self discharge over time. It is most likely to be an AGM battery.
Do you have information on the brand/model number of the battery? Without knowing this you won't be able to tell the type of electrolyte format (ie AGM, GEL,...). You might be able to determine this by physical inspection of the battery. Does it slosh when you move it from side to side? If so it is FLD (flooded or wet cell). Are there any vents or ports on the battery? AGM and GEL are hard to tell apart by inspection.
Additionally, you need to ensure that the inverter is supplying current at a reasonable level for the battery. You don't want to charge it too hard as this can damage the battery, but charging too slowly will take a very long time.
Assuming this is a vehicle battery (or similar medium size lead acid cell) then you'd be looking at an 8-10 hour charge time from dead flat to full. Take the capacity in Ah, divide by Amps supplied by your charger and that will give you the hours to charge from empty to full. The key thing with both AGM and GEL cell batteries is to prevent over charging. If your charger has an automatic cutoff then this should be fine, otherwise you will have to monitor closely.
Hope this helps.