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Battery drained...calling battery experts

Old 07-31-2019, 07:22 AM
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Default Battery drained...calling battery experts

My marina left my boats power switch on when they stored it about a week ago. There was enough power to turn the motor, but after about 15 minutes cruise, my gps/sonar screen began to fade and my radio went out telling me the primary battery was dead. My backup battery seemed fine.

this battery is a Gp 31 AGM (sams Duracell) that I installed a year ago. Iím charging it now. My question is will there still be adequate life in this battery after charge, or should I go ahead and replace it? Canít recall if AGMís can recover after a significant discharge like this. Thanks
Old 07-31-2019, 10:31 AM
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Batteries do not like being fully discharged and, even if it 'takes a charge', the capacity and longevity are likely to be significantly reduced.

If the marina was supposed to turn the battery switch off, I would ask them to assist in the cost of the replacement. JMHO
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Old 07-31-2019, 11:46 AM
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If there was enough power to start the engine it probably wasn't that low. Most modern electronics shut off to protect themselves from low voltage long before the battery is completely depleted, usually around 10.8 volts. I think it will be fine.
Old 07-31-2019, 12:01 PM
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If there was enough power to start and run the motor and radio & MFD for 15 minutes, it sounds like the charging system is not charging that battery, but the battery may have been OK..
The battery still may have been damaged by that recent deep discharge on your run if everything was being powered by solely by the battery and not the alternator/stator charge system.
After you fully charge that AGM if it will accept it, have it conductance-tested and possibly resistance load tested at any auto parts or other 12v battery store to see what present CCA capacity is compared to the original spec for that on the case label. Test seprately on both studs and posts as the results may be surprisingly different.

Is there a Black negative "daisy-chain" battery cable in place between the 2 batteries' negative cables so both will charge from the engine, not just discharge to a load?
Old 07-31-2019, 02:04 PM
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Thanks for the replies...i think I will see how it runs before replacing it. Ttaxi I will have to investigate the daisy chain.
Old 08-01-2019, 05:09 AM
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I agree root of the problem doesn't seem to be battery, but rather the wiring and/or the charging system. How many batteries and how are they wired? is the battery that powers the gps the same as the one that cranks the engine? if there are multiple battery banks, how are they charged when underway?
Old 08-01-2019, 05:16 AM
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If it is the battery, I think those have an 18 month replacement warranty.
Old 08-01-2019, 05:19 AM
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with a properly operating electrical system, with the engine running it is the alternator(s) supplying energy for the boat, not the battery. if the battery is bad here it is almost certainly because it isn't/hasn't been being charged correctly.
Old 08-01-2019, 05:25 AM
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My GF left the battery switch on for my port battery "the one all of the electronics are tied to" and it did the same thing. It won't hold a charge. I can leave it hooked to the charger for a week and it barely charges enough to start the boat. Then once I'm trolling for a while, my electronics start shutting down and the stereo starts pulsing. I replaced the batteries "8 year old Sears Platinum" and added an onboard charger and the problem is solved.
Old 08-01-2019, 06:00 AM
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AGM's can be drained completely without damage. Lead acid cannot.
Old 08-01-2019, 07:28 AM
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Copied from Opimas sight:

This is a recovery method for the do-it-yourselfer using the equipment you've got in the garage. With this option, you're going to trick your traditional charger into charging the deeply discharged AGM battery.

Here's what you need:
  • Battery charger (under 15 amps)
  • Jumper cables
  • A good battery, preferably above 12.2 volts. (It can be an AGM or flooded battery- it doesn't matter.)
  • The seemingly dead, deeply discharged AGM battery
  • A voltage meter
  • A watch or timer
Now, here's what you do:

Hook up the good battery and deeply discharged AGM battery in parallel – positive to positive and negative to negative. Do not have the charger connected to the battery or turned on at this stage.

Now, hook up the good battery to the charger. Turn on the charger. The charger will "see" the voltage of the good battery (hooked up in parallel), and start providing a charge.

After the batteries have been hooked up for about an hour, check to see if the AGM battery is slightly warm or hot to the touch. Batteries naturally become warm during charging, but excessive heat may be an indication that there really is something wrong with the battery. Discontinue charging immediately if the battery is hot to the touch. Also discontinue the process if you hear the battery "gassing" — a hissing sound coming from the safety valves. If it's hot or gassing, STOP CHARGING IMMEDIATELY!

With your voltage meter, check back often to see if the AGM battery has charged to 10.5 volts or above. This generally takes less than two hours with a 10-amp charger. If it has, disconnect the charger from the wall outlet and remove the good battery from the charger. Now, connect only the deeply discharged AGM battery to the charger. Turn on the charger and continue until the AGM battery reaches a full charge, or until the automatic charger completes the charge process. In most cases, the AGM battery will be recovered.
Old 08-01-2019, 12:12 PM
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Originally Posted by Pure Luck View Post
My GF left the battery switch on for my port battery "the one all of the electronics are tied to" and it did the same thing. It won't hold a charge. I can leave it hooked to the charger for a week and it barely charges enough to start the boat. Then once I'm trolling for a while, my electronics start shutting down and the stereo starts pulsing. I replaced the batteries "8 year old Sears Platinum" and added an onboard charger and the problem is solved.
maybe your symptom disappeared, but the problem is likely still there. sounds like you're discharging your batteries even w/the engine running at trolling speed. not a good thing. a new battery can mask it...for a while. but this is not a well designed and functioning electrical system.
Old 08-01-2019, 12:18 PM
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Originally Posted by chainsaw42 View Post
maybe your symptom disappeared, but the problem is likely still there. sounds like you're discharging your batteries even w/the engine running at trolling speed. not a good thing. a new battery can mask it...for a while. but this is not a well designed and functioning electrical system.
From looking at the voltage when it would happen, it seems the battery would drop a cell causing the voltage to drop way below 12vdc and shut everything down. I guess I'll find out if there is another problem besides that. I'll put my clamp meter in line of the new batteries and see what the charging current is when Idling. That'll be an easy way to see if I really have a charging problem or if I just had a battery problem.
Old 08-01-2019, 12:34 PM
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Originally Posted by Pure Luck View Post
From looking at the voltage when it would happen, it seems the battery would drop a cell causing the voltage to drop way below 12vdc and shut everything down. I guess I'll find out if there is another problem besides that. I'll put my clamp meter in line of the new batteries and see what the charging current is when Idling. That'll be an easy way to see if I really have a charging problem or if I just had a battery problem.
turn all the stuff on you usually run (sonar/gps/radio/whatever). if the voltage at the battery terminals is at or very near 13v, you're essentially 'breaking even'...if it's below 13v you're discharging, above 13v you're charging (rough numbers). you'd like to see it at about 14.3v meaning the battery is seeing 'full' charge voltage. my guess based on what you said is that you'll be below 13v at idle w/a bunch of stuff turned on.

OP could do the same thing.
Old 08-01-2019, 01:10 PM
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Originally Posted by chainsaw42 View Post
turn all the stuff on you usually run (sonar/gps/radio/whatever). if the voltage at the battery terminals is at or very near 13v, you're essentially 'breaking even'...if it's below 13v you're discharging, above 13v you're charging (rough numbers). you'd like to see it at about 14.3v meaning the battery is seeing 'full' charge voltage. my guess based on what you said is that you'll be below 13v at idle w/a bunch of stuff turned on.

OP could do the same thing.
It was dropping to 8 or 9ish with everything on after a bit, then it'd bump back up to 12ish after the load was gone. Guessing it was dropping a cell, then once the load was gone, the alt would bring it back to 12ish. That's why I bought new batteries.
Old 08-01-2019, 01:31 PM
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Originally Posted by Pure Luck View Post
It was dropping to 8 or 9ish with everything on after a bit, then it'd bump back up to 12ish after the load was gone. Guessing it was dropping a cell, then once the load was gone, the alt would bring it back to 12ish. That's why I bought new batteries.
not clear if you're talking about some voltmeter at the dash, a DMM at the battery terminals, or? (sorry if I missed it)

what we're talking about here is an accurate voltage measurement directly at the battery terminals.
Old 08-02-2019, 04:55 AM
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Originally Posted by chainsaw42 View Post
not clear if you're talking about some voltmeter at the dash, a DMM at the battery terminals, or? (sorry if I missed it)

what we're talking about here is an accurate voltage measurement directly at the battery terminals.
Using my DMM, Fluke 179.
Old 08-07-2019, 06:01 PM
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To follow up...

i gave the battery a good charge and went on my trip. The battery didnít miss a beat and seemed well charged the entire week. I even forgot and left the power on one night. It seems this AGM battery could be revived from the deep discharge.

still not sure my alternator is charging it appropriately though

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