which dual bank onboard charger?

Promariner ProSport Series

 

Ditto on the Pro Sport series. I just replaced a ProSport12 Generation 1 which lasted 10 years in a semi-exposed mounting and it did a great job of maintaining the wet cell dedicated pair of troller batts on my 17' skiff (that skiffs troller is a non-digital 5 speed so it sucked down a lot of juice during a long day on the water)

Pro Mariner makes a great product at a fair price, but which size charger is right for your use depends on what type of batts you have and how you run them: Wet cells are good (and will live longer) with lower amperage chargers - 4-6 amps per battery will fully recharge 50% discharges in 12-24 hrs if you can afford that time. 12-20A per cell chargers will obviously recharge a wet cell faster, but will also reduce its service life.

AGM's like a bigger output - 12 -20A per cell is good for best battery life and of course faster recharge times. AGM's will have a shorter life with lower amp chargers

My replacement charger is another ProSport, the Pro8 Generation 3 this time - its retains the distribution on demand and equalization charge of their earlier chargers (which do work and are effective) and adds in cooler operation, 50% lighter weight and a good led status display.
So yes, I liked Pro Mariner's build quality and performance enough to buy another one.