Motor help - PLEASE!

[flyfish]

Remember, the voltage doesn't totally determine your starting power. As your battery gets old it will hold a short 12v charge but will lose the ability to deliver the required amperage to turn the motor. I'm not going to pretend to know how all of it works, but know I've started my boat at 10 volts many times.

Easy fix. Go get a $70 battery from Walmart.

[JCsHOOK]

Just pull the cables off the battery in question and connect the car battery to the boat cables with your jumpers. This will tell you if that battery is the problem. JC

[artcarney_agr]

Did you check the fluid levels in all the cells? Have you maintained those levels?
How old is the battery?

Sound like maybe the battery has developed a "memory" and although reads that it's charged, it really isn't and discharges very quickly...very common for old worn out batteries to do this.

There's a voltage drop when you put a battery under load.....that's why lights dim (like runnning lights) when you crank the motor. Just because it's showing over 12 volts doesn't mean that's actually what it's putting out under load.