Batteries not staying charged

[3006]

Hello all, new member here. I have tried to do a search for this issue but wasn't successful. I have a 2012 tri-toon with a mercury 150. It has dual batteries but no selector switch. It does have an onboard charging system. The issues I have had is, one trip out the boat wouldn't start while out on the water, the batteries were dead and I had to get towed in. This past weekend the boat died while driving and wouldn't restart, had to get towed in. I had the batteries checked and both are good.
It sounds to me that the alternator is not charging the batteries while driving and once the batteries drain down it won't restart or it will die. Has anyone had this kind of issue before?
Thanks for your time and I have found the forum to be really helpful!

[lakerunner]

I would be talking to my Merc dealer soon

[Strake]

I would agree with your assessment that the charging system of the engine isn't charging your batteries..... BUT I would strongly encourage you to invest in a battery switch. At least you won't drain BOTH batteries should something come up in the future, after you get it repaired.

[MH Hawker]

it may not be charging, but it runs from a separate voltage source, so you may have 2 problems

[BobL]

Sounds like you may have multiple issues.

A - You said you have an on board charger? Are you plugging this in and it is not charging the batteries? If yes, that is issue 1.

B - If the batteries are being depleted quickly, something is drawing them down when not in use.

C - Your engine is not charging the batteries when running.

Here is my $0.02.

1 - As suggested, get a battery switch NOW. The switch needs to be have "1, 2, Both, Off" options.

2 - I don't want to get into a battery debate but over the years (of reading and personal experience) I have come to the following conclusions. In my opinion Batt 1 should be a used for cranking and should be a cranking battery, Batt 2 should be used for accessories (i.e. stereo, trolling motor, etc.) and should be a Deep Cycle battery. Never run in Both position if Batt 1 and Batt 2 are dissimilar in type and age. When you stop the boat and listen to tunes or troll or whatever, switch to Batt 2. When you are ready to leave, switch back to Batt 1 and crank the boat.

Did your dealer install the second battery or did you do it?

How are the batteries wired?

If your dealer did not install the second battery then you may consider taking battery two out of the boat and wire it for only one battery when you bring it to the dealer for repair. I cannot promise you that they will try to blame you or your setup for the charging system failure but that is a precaution I would take.

[C_M_25]

1. You have to get a switch.

2. The charging systems on these motors are not an altenator type system like you car (assuming outboard motor) so they will not provide a lot of charge unless you are running for a long time. Also, you have two batteries that are being charged simultaneously from the motor, so it will only provide a minimal charge to the system.

3. You may have a battery with a bad cell. Even new batteries can be bad. Pull them and take them to oreillys to be tested. Depending on how the batteries are connected, they will act as one 12 v battery sharing voltage between them. The weaker battery will draw down the voltage.

4. You have a voltage draw on your boat when off. Check and make sure none of the switches are on.

5. How to test. With the boat on, take a voltmeter and check to see if you are getting charging voltage to the batteries.

[rancherlee]

Make sure the batteries are good also if it ends up being the Alternator/Stator. Weak batteries will put a huge strain on and can kill an new alternator/stator. I'm assuming you have at least a 40amp alternator/stator on a modern 150hp outboard which is more than enough to charge 2 batteries and run all the accessories short of a 2000w stereo system. The EFI system will draw 20-30amps off a battery which will only give you around 2 hours of run time on a fully charged battery if the alternator is bad.

[3006]

Thanks for all the responses and advice. The batteries were both installed from the dealer. I had them both checked and they are good. I pulled the alternator off and had it checked and it is bad. I will be installing a switch for the batteries!
Thanks again.....