Problems starting, don't think it's the battery

by Dennis

I'll try not to confuse people here, but I know the more specific the better chance of troubleshooting. I have a 50HP 4 stroke Mercury on a pontoon boat. My wife went to start and the motor turned over like twice, but then the battery was dead (or at least power). They put another battery in, it started, they made it about 50 yards and it died. She tried to restart, nothing, made sure neutral, still nothing, so she go towed home. Later in the night she thought she'd try the boat again and it started, but kept it tied up. I came home checked the voltage on the first battery and it was like 12.3V. Put it on the charger and got it to 12.8, so I put it on the boat. Motor started, turned it off. Next day nothing. Pulled the battery and it shows 12.5V. Threw the 2nd battery on to see and it starts but I disconnected everything. I used to have a problem with something draining the battery, or kids playing with switches, so I never hook up the accessary wires, just the 2 main cables. So I can't understand if I have a drain with just those 2 hooked up. But with the battery showing OK voltage, why the intermitant starting or dying? Is there something in the gear shift regarding neutral, or something electrical in the motor? It's really a pain to go find a trailor and get it in, so I'm hoping to be able to troubleshoot. Thanks