Nissan 50hp TLDI Alternator problems?

[thelucky111]

Just bought a new Optima battery, all worked good for 6 hrs of trolling but battery is really low already?
Could I have an Alternator problem?

 

[pvanv]

Possible. Could also be a bad battery, or wiring issue. What is the voltage at the battery, both running and stopped? I would troubleshoot.