Battery issue

Pat310

While heading out for a nice fall boat ride, about 20 minutes in, I started losing voltage on both start batteries. Quick U turn and hit the throttles. Voltage at about 10.7 by the time I hit the no wake zone.  Alarms blaring. By the time I get tied up, down to about 9 volts. House battery stayed at 13 volts.  Plug in shore power, tuned on battery charger but voltage kept dropping. Had a commitment and shut off batteries and shore power before leaving. Any ideas?  I’m thinking maybe battery isolator that it affected both start batteries. It is the original from 2003

Ian

Both of mine crapped out after 2 seasons all of a sudden - similar symptoms. replaced these AGM’s with sealed wet again.

Pat310

All 3 batteries replaced this spring

raybo3

Alternator???? 

Dream_Inn

raybo3 said:

Alternator???? 

Two of them?  I'd think more the isolator.  Curious if charger got them back up and fully charged.

LaRea

They aren't getting charged by either source (charger or alternators), so I agree the isolator is the prime suspect.  

davidbrooks

What happens if you take them out and throw them on a car battery charger?

PickleRick

davidbrooks said:

What happens if you take them out and throw them on a car battery charger?

They lose their sea legs 

PickleRick

raybo3 said:

Alternator???? 

I'd also start here but only because I don't know how to test a isolator without looking it up.  While two dying at one would be rare, they both need to see 12v signal from the switch to activate.  

rasbury

Won't the gauge show charging voltage? I've heard and should research if AGM batteries get o the dead to low voltage side they don't charge properly.  This is from an EMS dept I deal with..

Pat310

They are flooded acid batteries. At the boat yesterday found the 2 60 amp breakers for the start batteries had popped. This kept both the charger and the alternators from charging the batteries. Now i need to figure out what made both of them pop. Thinking bad battery because charged the batteries overnight and when i turned off charger the voltage on the dash dropped 1 volt in about 5 minutes. Could completely dead battery trip the breakers when charger kicks on?

Formulaben

Pat310 said:

Could completely dead battery trip the breakers when charger kicks on?

I think you're on the right path making sure it's not bad batteries.  Are you sure it was the charger and not the alternator that popped the breakers?  Absolutely it can with the alternator.  A "dumb" alternator will give it all that it has once it's up and running.  

When the battery is heavily discharged it'll take up any spare amps available, and when the alternator reaches a point where it can deliver enough amps (at higher RPMs, leaving the no-wake zone), the batteries will suck up all that is available, which can exceed the 60 amp breaker capacity.

The solution is to charge the batteries with a smart charger first, assuming that they aren't damaged, but I'd definitely be suspect of them if they got that dead.  A flooded lead-acid battery can be severely damaged if discharged below 10.5 volts.

Pat310

@Formulaben that was my thought. 70 amp alternators and I believe I had left the charger on when I started the boat throwing another 30 amps at it. Marina that installed the batteries in the spring will load test them Monday.

PickleRick

I don't work with marine batteries but at my shop I'm seeing far more new battery failures than I used to.  Had to argue with my distributor to get both in my 7.3 exchanged.  Tried to claim I had a charging issue.  I have a digital read out display that reads things like EGT, boost pressure, hpop pressure and changing.  I can even see my injector duty cycle, oil temp and intake air temps.  Things you need for towing at or above max towing capacity.