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Do you have an idea what your loads are during the day?
Lowest cost will be if PV can cover your loads easily and still charge battery. Remember while loads are connected to the Axpert and it is switched on you use about 900Wh per 24hrs just to keep it running.
If running from PV mostly during the day the option to just use battery for brief periods is fine.

I used to have the axpert, 
my settings were as follows 
SBU ) to charge the batteries 
if loadshedding hit or cloudy then I would change this setting to UtIlity to charge 
I had an old laptop with chrome remote desktop connected to the inverter via rs485 cable and multisibcontrol.net so I could change settings instantly on the inverter from my phone. 
 
Then I would run the battery down to 48 v daily and wait for Solar to charge up again in the morning. Saved money like this 

The best solution it to get something like Solar Assistant. This will allow you to control everything and monitor remotely and also make changes.
 

+1 - Runs my system perfectly - I have a very similar setup to yours and I have reduced consumption from 30Kwh/day to around 16Kwh/day.  All automated and easily changed when loadshedding is going to happen.

Use SBU as @BryanOC6suggests, that will mean your loads will be run from the panels first, then the battery and then from grid.
You can then use the 'back to grid' setting to control how much battery you want to use to save some for load shedding and 'back to battery' to decide how much you want to charge from grid.
When there is no sun and load shedding you will use the battery down to the 'cutoff' setting which can be 90% DOD.
Use 'back to grid' for this, don't take it down to 90% all the time of you might end up with nothing for load shedding.
This can also be controlled with 'back to grid'.
This is up to you to decide if you want to save on electricity or have the battery last longer, but you have to always think of the sneaky load shedding that can pop it's head up any time, so it's better to keep some battery storage by switching 'back to grid' with enough to spare depending how much you need to get through a session of LS.
Good luck, it takes a little fiddling with settings to get the axpert running smoothly depending on your specific needs, but once set up correctly you should be able to forget about it.