Mercury Optimax Voltage problem

[Cawagu]

First, a little background.........I have a 2013 Optimax that is powered by a DelStar (1075 CA) battery, which also runs all my electronics aside from my trolling motor. I keep it on a dual pro charging system when not in use and it shows full charge every time I check it. I've also put a meter on the terminals and show 12.7v, and have had a dealer put a load tester on the battery and it shows it holds a charge and the battery is good. I have Smartcraft SC1000 speedo gauges and run 2-Lowrance HDS12 touch units.

My problem..........When I hit the water and launch the boat, the first time cranking the engine over, I get a low voltage alarm from the engine. I've witnessed on my smartcraft and also on my Lowrance, the voltage will drop to 9v as it's turning over. It sounds the alarm, but the engine will start, a little rev, and it keeps running fine. Once its running the voltage will climb to 13.8v. Throughout the day of fishing, I'll run live wells, Lowrance units, etc and the engine will crank without issue (it does however start first turn over, compared to multiple turn overs on the initial start up at the launch). If I stay in one area for several hours without cranking and moving, I have experienced the same voltage alarm when I go to crank up to leave. I always keep the voltage readout on the unit near my feet and have never seen it get below 11.5v while fishing.

Can I be experiencing a problem with the engine? I thought maybe alternator, but seems to me like the volts wouldn't rise while running if it was that. However, I am by no means a mechanic!

Thanks in advance

 

[GA_Boater]

First thing - Welcome aboard.

Second thing - When did this problem start? From the time you got her or it just showed up?

Third thing - On the first start of the day, what electronics/electrical gear is turned on?

Fourth thing - With the voltage dropping to 11.5 volts while fishing, the battery is pretty much dead. How long does it take to reach 11.5V?

Fifth thing - You need to split some of the house load to the deep cycle battery to run the Lowrance, live wells, etc. You're asking a lot of the starting battery. Maybe keep the Lowrance units on the starting battery because of interference.

Sixth thing - Clean every positive and negative connection from the battery to the motor and +/- leads off the battery. Shiny, bright is what we like to say.

Lets see what others have to say and hope this helps a little.

 

[Cawagu]

1. Thanks
2. This just started about a month ago
3. Typically, nothing is on. I've only started the Lowrance once to watch on the display if the voltage supply to the unit was also dropping, and it indeed was.
4. It usually takes 4 to 5 hours of fishing to drop to 11.5v. I'm really hoping that it's the battery, but I brought it in and they said it was good when load tested to 1100amps.
5. I understand & I'm not disagreeing, however I have buddies that run the same engine and all same load on a single battery and they don't have any issues.
6. I will try cleaning the post and see.

Also, another bit of information. I've pulled the kill switch and had someone turn the engine over while I held a volt meter on the battery post, and it drops to about 10.3v while turning over.

Thanks again for the response and help.