The 24 series is "wet cell" (lead acid) type. Since you know where the settings are, why not just switch to the correct battery type?
From reading the Inverter manual, when you select Gel type battery, the charging rate is lower than for other battery types. The chart in my manual (below) shows the charging rate to be lower - but that chart is in the section for "deep cycle batteries" and the Series 24 is not a deep cycle (it is a chassis battery).