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Dual Battery start issues


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I replaced my boats dual battery set up this year with 1 12v 27 deep cycle and 1 12v 24 high cold crank amp battery. The boat had dual 12v 24 batteries prior but I wanted to switch one out for listening to the stereo while out on the water. Batt 2 on my perko switch is the high cold crank battery that I have been using to start the boat and batt 1 for running the stereo. I’ve noticed on the last trip that the boat was having trouble cranking on batt 2 and I had to switch to batt 1+2 to get it to turn over... Batt 2 got to the point where it wouldn’t even run the blower...so I’m thinking bad battery since my amp meter is showing 13-14v on the dash when the boat is running. Well I took the battery back to Oriely and had them test it, told them it was dead. They told me it would take about 2 hours to recharge before they could test it and they’d call me. 10min after I left they called and said the battery was charged and showing 14v, no problems. So my question is, in my set up what would cause Batt 2 to be unable to start the boat? There is a PAC-200 battery isolator installed with the switch also. 

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Sounds like you are not charging the battery.  So I'd be checking the alternator wiring and any breakers/fuses/fusible links that might be between the battery and the alternator.  Sounds like at a minimum the dash is seeing the alternator voltage.

 

Easiest test would be to start it up on Battery 2 and then stick a voltmeter on the terminals of battery 2 and see what you have for voltage when the boat is running.

Edited by oldjeep
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3 minutes ago, oldjeep said:

Sounds like you are not charging the battery.  So I'd be checking the alternator wiring and any breakers/fuses/fusible links that might be between the battery and the alternator.  Sounds like at a minimum the dash is seeing the alternator voltage.

 

Easiest test would be to start it up on Battery 2 and then stick a voltmeter on the terminals of battery 2 and see what you have for voltage when the boat is running.

Ok, I’ll start there. That was my first inclination too but thought it was strange that they were able to get the battery charged back up to test that quickly and that it was at 14v after being seemingly dead. 

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2 hours ago, FlightTime said:

Ok, I’ll start there. That was my first inclination too but thought it was strange that they were able to get the battery charged back up to test that quickly and that it was at 14v after being seemingly dead. 

Yeah, I don’t understand dead to 14v.  Maybe your contact at oreilly AP has not yet been trained on batteries. 

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Check to see if the large ground cable linking the battery 1 and battery 2 negative terminals is loose or disconnected. 

It is difficult for the alternator to maintain let alone recharge two batteries when they are under heavy use.  After I installed and regularly used an onboard battery charger I stopped having battery charging issues.

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