Battery drain, Mariner 40EL (2-stroke 2 cylinder)- help diagnose please?

[SAABologist]

Thanks in advance for pointers--
My old Mirrocraft with Mariner 40 EL 2-stroke has a battery drain problem. Here are some things I've noticed:

- Battery charges fine when underway, voltmeter reads going up to 12.2 volts while running.
- The battery will drain really fast when parked. Fast being a few hours dropping from 11.4 to 9.6 V
- All accessories work fine and there are not many (6 in all) - Garmin Striker, stern/anchor light, bilge pump, livewell, voltmeter, USB/USB-c charger. Only the voltmeter and USB ports stay on.
- If i disconnect battery after stopping, it stays charged.
- Motor cranks fine at 10.7 V and above.

Questions:
- Is there sometihng inside the motor I should check? Inspection of all wires and connections look fine. Only a little moisture inside the cowling.
- Could this be the wiring of the ignition and safety kill switch? How to diagnose?

Thanks much,

 

[Pappy]

First off. 12.2v is not a satisfactory charge level. Should be way up into the 13v range. So, right off the bat you either have a drain and the engine cannot keep up or a bad battery or an onboard drain on the battery or a faulty engine charging system but we cannot assume anything yet.
Disconnect everything off of the battery.....everything. Fully charge the battery with a portable charger, check the voltage level of the battery once charged and the charger disconnected. Check again in the morning. What voltage level is the battery at. This will give us a base line to go from rather than automatically pointing a finger at the engine.

 

[airshot]

Agree with Pappy....a full battery is 12.6 volts and higher, under 12 volts is a dead battery ( based on digital VM)
Most engines charge at 13 plus volts. Test your battery !!

 

[SAABologist]

OK, will do. It's a 100ah deep cycle that is over 4 y old. I will charge it with a charger today and let it sit and check it tomorrow. Thanks,

 

[Pappy]

With nothing else attached to the battery !!!!!
Take a voltage measurement tonight and again in the morning or tomorrow sometime.