Twin 150s issue - any ideas?

I've got twin 2013 150s on my center console and have never had one quit until last night.

Started up both like a charm and idled for a few minutes. One sounded like it was making a little bit more noise than usual. Almost like white noise, but different enough that I noticed. Then it wound down and quit. I tried to start it back up but got low battery warnings and it wouldn't crank hard enough to turn over. Trying a few combinations of batter switches didn't change anything.

Any ideas where to start? Help is much appreciated!

I tried to start it back up but got low battery warnings and it wouldn't crank hard enough to turn over.

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I'm sure it's not this, but one battery on my 225 couldn't turn it over the other day after the lower unit had lunched itself and the gears were mashed together. Hopefully your batteries are just a bit tired but I would have thought that if the other engine was running there should be enough power.

A little more info is needed.
I guess you are running a two battery set up (1 per motor) but need to make sure. I don't know much about tandem set ups but remember reading here that if you only run one bat that 1 motor won't see it or something that leads to charging/ running problems.
Also where did you hear your noise? Block, starter, leg, flywheel? With the HT leads off the plugs or even better with the plugs out can you turn the motor by hand. Can you turn the motor with a fresh battery with only the motor in question connected. Ie nothing else other than the motor connected.
Are all battery terminals, motor earths, connectors cleaned to give good resistance free contact?

these are at least the more obvious places to start eliminating problems.
Once this is all done let us know how you get on.
good luck.
Dean.