2006 Mercury 200 Optimax Voltage gremlin

[Jim285pro]

Serial#1B432643
New to me boat and this issue has been present since day 1. While on plane above 4k RPMs I get voltage spikes around 16V. It doesnt do it all the time, only when the cranking battery (NEW 125AH Ionic Lithium) seems to be charged fully. If I stop and fish a while and then move It wont do it and the voltage stays around 14.2-14.8. But if I stay on plane and run about 10-15 minutes I can watch the voltage creep up and eventually start spiking between the 14.5-16. It causes my electronics to shutoff from over voltage. When its spiking it will run up to the 16V for about two seconds then down to 14 for two seconds then back up. The spikes never occur at idle.
Things I have done-
-Triple checked connections and verified tight and corrosion free.
-Purchased service manual and diagnosed Alternator, It tested good at shop but they lacked the ability to spin it to higher RPMS to test fully. I replaced with brand new OEM altenator.
-Fuseable 100A link tests good and visually looks good.
- I have ohm tested the red and purple wires from the alternator and have traced them all the way through harness and they visually look good and test good.
-Red bullet connection is tight and verified through ohm testing.
-Checked fuses in motor that red wire runs to. They are good.
I dont know where else to look at this point.

[lpugh]

I would swap out that battery for testing purposes first to be sure the BMS in battery is not going into shutdown mode for some reason as that or any poor connection would cause that symptom such as either battery cable connections on battery or motor

[EuropeanAM]

I would swap out that battery for testing purposes first to be sure the BMS in battery is not going into shutdown mode for some reason as that or any poor connection would cause that symptom such as either battery cable connections on battery or motor

I tend to concur with this suggestion.

Additionally, are you using a battery switch OR any type of multi-battery "on the fly" charging system?

[Jim285pro]

I tend to concur with this suggestion.

Additionally, are you using a battery switch OR any type of multi-battery "on the fly" charging system?

I have switches but none are connected to the big motor. Hot and ground are direct to the battery. No charge on the fly systems.

[EuropeanAM]

If you have indeed tried a NEW, OEM Alternator that was installed properly:

-Check battery cable connections at BOTH ends of the cables (make sure they are not loose at the engine)

-Try a totally separate, properly rated battery (Wet cell or AGM with 950+ CCA).

[Jim285pro]

If you have indeed tried a NEW, OEM Alternator that was installed properly:

-Check battery cable connections at BOTH ends of the cables (make sure they are not loose at the engine)

-Try a totally separate, properly rated battery (Wet cell or AGM with 950+ CCA).

I will try a different battery and let you know. Thanks for the replies. Ive checked connections numerous times and went ahead and redid them all before last time out.

[EuropeanAM]

Don't overlook the ground strap for the alternator.

If this continues- you will likely need a (or another) NEW OEM alternator.