ed, do you have a multimeter, or access to it?
next time your out on your boat, test each battery to read your volts before you drive it to the launch to go out. If you trickle charge you should read normal 12-13v. next, once on the water with the motor running, confirm your low voltage by directly checking alternator (red test to red terminal on alternator and black test to frame ground or anything except the alternator) If it is in fact low just as your display shows, then test each battery while the engine is running, they should be 12-13. Finally, turn off your engine and test your batteries to see if there is any drop (less than 12 immediately probably means bad batteries) Test batteries again after they have been sitting a while (30+ minutes) and see what each read. If your batteries have drained at all, then its probably your batteries, if they have held their charge, then it sounds like your alternator, assuming you have no major draws from your amps and margarita maker
