Recent battery temperature data on my AGM shows it likes to stay well above ambient temperatures when in constant use, charging or discharging, and hot ambient temperatures have battery temperature much higher than the expected linear relationship.
I think the PD9280 is a bad choice for your smaller Gel batteries.
I do believe it will seek 14.4v initially, at full 80 amp output or nearly so, and once it gets to 14.4v at output terminals, amps will then taper. I thought PD's claimed current limiting was to protect the PD, not the battery.
I am not sure the best ways to plug the pd9280's 20 amp plug into various sources, and think any effort to do so will be in vain on your specific capacity of Gel battery.
Perhaps your PD9280 score, could find a home where its ability can be better realized