Battery/Voltage alarm/rough start problem

I’ve started having voltage alarm problems with one of my batteries/motor. Voltmeter shows 12.62volts. I’ve undone, checked and re-tightened all terminals and alarm still comes on when starting. The motor will race to over 2000rpm and then will often stall. It is only doing this with dedicated start battery (Seamaster Gold M70). My other battery AC-Delco (dual purpose) will start motor fine. Could there be a problem in the isolator? Could it be the Seamaster is slightly under specs for my motor (175hp Suzuki four stroke). The AC-Delco is 830Cca, 110AH and 200min RC whereas Seamaster is only 720cca, 95AH and 160min RC? Buggers me🤔

funny this should come up, my mate has a 150 e-tec, and it will only run one one particular battery, connecting up any other battery, including the new identical one he bought, the motor misses and splutters, can't explain it, the tach also jumps around, kind of indicating a regulator issue, but, put the old original battery on, it runs like a dream, got me buggered.

In both cases ( Barra and Noel ),
Is the second battery via a changeover switch ?
Could be a bad connection in the switch or wiring.
Or is there some sort of coating on the second battery post causing a poor connection?


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In my mates boat, the second battery was via a switch, but for testing purposes, we connected direct, one battery works a treat, the second battery causes the motor to miss and splitter, and the tach jump mad, purchased a brand new battery, same result, the new one causes missing and tachometer jumping, old battery is perfect, got me beat.

That's a good one,
Got me thinking alright ?
Too late now, but I'd put a meter on each battery after they were connected and the motor is running and see what the voltage is like.
That might point you to what's going on ?
Could be like you say the regulator ?
I don't know these motors I'm just going by electrical troubleshooting, the regulator would be inbuilt within the alternator, could the new/2nd battery need a charge ? I'm suggesting the alternator could be failing under load.


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I’m not much of a mechanic but Pulling apart the changeover isolator switch is my next check. The suspect battery was fully charged before trying to start motor and the times the motor doesn’t snuff out the multimeter reads 14.8volts at idle. Maybe the dreaded Suzuki white wire perhaps?
But then wouldn’t that be the case with the second battery also as the wires from motor feeds into battery selector switch? 🤔😩

Barra if you can, an easy check ( before you start dismantling anything) and if you do have an isolator switch all wired up to the two batteries is swap the batteries over so the battery that you know did work ok is in the second isolator position. That will sort out if the isolator switch or battery wiring is the issue.


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The easiest & fastest way to find out what's wrong is by taking Voltage measurements throughout the system while the motor is cranking over.
You may have to disable the ignition to stop it starting to give you time to get the readings.
Start at the battery posts & work your way out.

Out of interest, what is your white wire connected to?

So had the suspect battery load tested=all fine. So had a look behind the isolator and all cable connections were fine with no sign of corrosion. Took the positive power lead fthat goes from switch back to motor and put it direct to battery and motor started fine with no voltage alarm. Must be contacts inside the switch itself. Will replace the battery switch as well as the positive lead going from switch to positive terminal as it has signs of the green corrosive death.

Good work barra, if you have the time, why not replace 1 thing at a time, like the cheapest and easiest part - the positive lead ? Might save the unnecessary cost of a replacement switch. Just an idea ,,,


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