I've been pretty happy after 2 years with a Minn Kota Portable MK110 I think is the model. 1 bank 10 amps, auto. If I remember correctly, they will handle the AGM batts as well with a selectable switch, but I'd check that on the MK site. Also might check out Dual Pro and Guest, they have a portable charger as well.
Not sure what you've got now, but for some reason, I never trusted the Ship n shore models from Schumaker. Had one blow a batt one time on me. And I mean blow! Probably my fault more than the charger though.
Wannabe...