Mercruiser 140 starting problem

[Greg PA]

My Mercruiser 140 struggles to turn over at times. I have two batteries in-line and everything is recent except the plugs (changing them next weekend). The started got wet a couple weeks ago (bad bilge float switch). It struggled to start yesterday, but finally fired up and I ran it for a couple hours off and on. Went to go home and she she wouldn't catch. Sounded like a dead battery, but they are less than a year old.
My thought are bad batteries or starter. Any other ideas?

 

[looseplay]

have you checked battery to see if you are getting correct volts, are your terminals dirty? Is you engine turning over or is starter just clicking

 

[Bt Doctur]

pull the spark plugs and check for water if it is hard to turn over.
battery cables, cable ends, starter brushes,binding.

 

[guyjg]

I have two batteries in-line...

Are they in series? A big NO! Are they parallel? They should be electronically isolated. If not the bad battery will suck the life out of the good one.

I'm surprized that the starter survived submersion; it may need to be remand.