The chemicals in the Batt need to be "Reved up" in order to make the Batts perform at their Best..

A Charge of 3 amps is cool for its First charge, then go and run it in the Boat being mindful that your Batts run time may only be a few minutes..
Run the Batt till there is a performance drop then Bring it in, take it home and Discharge it on your Discharger (a Triton Charger is good for this) Then rip 5 amps into them and all will be sweet.