I have not found any gel batteries that did not have lots of failures regardless of the brand. They are the worst possible value in terms of battery life for your dollar. I would send back the charger and get another one.
I download the user manuals for anything like this to see what it can and cannot do before buying it. I avoid a lot of grief and wasted time and money. This is also where a name brand unit that is commonly used in RV's is probably worth the additional cost. It is not something I would want to replace and then have to replace it with the replacement a year or two later or have it shorten the lives of my batteries.
The charging profile for a flooded lead acid type battery is different from that of an AGM. For something that is going to be continuously used to charge the batteries I would go with one that has the proper AGM setting.