Battery drain on Mercury Pro XS 2016 model

[havacman]

My son has an issue of the motor occasionally going to limp mode because battery voltage drops to the 11.4 volts or so on sensor. He had to replace 3 batteries in 1-1/2 years. Yes he runs the big graphs the two power poles but has a electrical cutoff switch that disconnects all voltage from the cranking battery while sitting, has on board charger that works correctly, mechanic at dealership has said the battery is good and the motor is charging correctly they have no idea what is causing the issue that has occurred several times of the limp mode during fishing days. He has also attached a meter in between the wire from battery to everything else and is not showing any battery amp drain while sitting. Not every trip but random trips. Even when this occurs the motor starts no problem or sign of battery issue. Any ideas? Thanks in advance!

[JOE54]

sounds like too small battery

[havacman]

It is a 1000 CC amp battery that is installed by the dealership service department so they wouldn’t put too small battery on that motor.

[EuropeanAM]

It is a 1000 CC amp battery that is installed by the dealership service department so they wouldn’t put too small battery on that motor.

Is that 1000 MCA, 1000 CA, or 1000 CCA? Three different ratings, and it does make a considerable difference.

WHICH ProXS (specifically) is this (Mercury doesn't use years... really need the Serial Number for accurate ID, but at least a HP rating would help).

Reeds Injectors

[havacman]

Is that 1000 MCA, 1000 CA, or 1000 CCA? Three different ratings, and it does make a considerable difference.

WHICH ProXS (specifically) is this (Mercury doesn't use years... really need the Serial Number for accurate ID, but at least a HP rating would help).

I will find out the serial number and the actual battery size. The motor is actually a 2017 250hp. I will post it soon as my son gets it to me. Thank you!