I have never used an onboard charger and am looking into one.  Anybody know what kind of specs and brands I should consider/

I have a dual pro in my boat. Just make sure if you have 3 batteries you get a 3 bank.look at the total amps and divide by 3 and thats will be your amps per batt. The reason that matters is because the more amps the faster your batteries will recover. mine will usually recover in less than 8 hrs.Try to get one with 15 amps per bank.

Make sure if you get one that it will be able to charge all your batteries....ie...3 batteries..get a 3 bank charger.