Macduffy

Hi @Coulomb @Solo
Following your advice I contacted the South African agent and he in turn got in contact with the OEM engineer. The engineer stated that the inverter follows a 2-step charge if it is above 12V and a 3-step charge if it is below 12V. I since reran the test and dropped the batteries down to 11.9V and then started the charge cycle, it went through the bulk charge stage and stayed at the absorption voltage for a number of hours and then finally entered the float stage. So this seems to have solved my problem, I wasn't draining the batteries low enough to enter the absorption stage. I have only tested this when setting 05 is set to AGM, which the agent advised. I am still to test it under the User Defined setting. 
I don't often drop the batteries to below 12V, so I may still keep the equalisation option active every few days/weeks just below the gassing voltage. I am still concerned I am only partially charging the batteries on the 2-step charge.....
On another note I looked further into the batteries that I previously bought that went bad - the Omnipower (OPR120-12) ones which lasted just over a year. I was told that most of these are sold as new, however are actually second hand and are taken from battery banks. The guys keep the box and then repackage them. One of the signs to look for is a serial code sticker stuck to the top of the battery over the original serial number. As it turns out my Omnipower batteries has a different serial number stuck over the original serial number and some of the digits vary - so I suspect I may have been sold old batteries. The shop I bought them from has since gone out of business so no option for recourse. On my new Ritar batteries I checked the voltage when I bought then (>12.7V) and checked the date of manufacture from the serial number (Aug 2019) - hopefully it is enough of a check to ensure I bought new batteries this time.