Murphy, the reason I choose the sentinel is they make a 7 amp automatic charger. ( based on their data it is similar to a standard 14 amp charger) weather that's true or not , I don't know, but they do charge relatively fast w/o overcharging.
http://soneil.com/12_volt.html the 1214S is what I have along with the battery tender ( 1.5 amps trickle)
You are correct a 3 amp trickle charger is not going to work for a larger battery bank or battery's that are run down quite a bit...which is not good for the battery anyway.