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Killing an AGM Battery

Old 09-02-2006, 09:38 AM
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Default Killing an AGM Battery

I accidentally have drained both of my Oddysee 1200T AGM Batteries twice. Left the stereo on with the volume off once for a week and worse yet left the bilge pump on manual for a week. Both times with the battery switch that I typically turn off was on both. Both times they charged right back up with no issue (I hope).

I have them wired so the motor will run on one but both get charged but I sometimes run both (I’m not sure why?). I also have them wired so only the bilge pumps work with the battery switch off.

I knew when I bought them this was a big issue. What can I expect, less battery life or total failure? Besides a brain transplant, what is the best device to keep from completely draining batteries?
Old 09-02-2006, 01:22 PM
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Default RE: Killing an AGM Battery

abysmal - 9/2/2006 10:38 AM

Besides a brain transplant, what is the best device to keep from completely draining batteries?
If you have to drain a batt way down, it's good they were AGM's as they bounce back better than any other kind....

batt switch off when you store/leave the boat....
Old 09-02-2006, 08:51 PM
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Default Re: Killing an AGM Battery

The battery life will be shortened. Hard to say how much. Generally batteries will last longest if you don't drain them more than 50% or below 12.3 for AGM (12.2 for flooded lead acid).

There are low battery cut off switches and low battery alarms. However the advice to turn off master switches is much less expensive.
Old 09-03-2006, 06:36 AM
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Default Re: Killing an AGM Battery

Would a good staging on board charger be in your budget?...........Keeps the batteries tip top all the time.
Old 09-03-2006, 07:33 AM
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Default Re: Killing an AGM Battery

Thanks for the responces.

I bought the AGMs so I would not need a charger (hold 99% charge for a year). She comes home fully charged and sits on a lift. She realy only needs the bilge pump for rainwater that seeps through to the otherwise dry bilge. I was trying to avoid having to connect to shore power. Not even a charger would have kept up with the bilge pump on manual. I'll investigate low battery cut off switches.

Thanks
Old 09-03-2006, 08:32 AM
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Default Re: Killing an AGM Battery

abysmal - 9/3/2006 8:33 AM

I'll investigate low battery cut off switches.

Thanks
this will work well as a batt cut-off switch - calibrate it for 12 volts and when the batt reaches 12 v, it will disconnect everything and save the batt....Wire it in-line on the positve lead....

http://www.bluesea.com/product.asp?Product_id=53476
Old 09-03-2006, 08:59 AM
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Default Re: Killing an AGM Battery

The big selling point on the AGM's is that they can take abuse without a problem. I doubt you hurt them at all. Most come with a 5 year pro-rated warranty.
Old 09-03-2006, 10:25 PM
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Default Re: Killing an AGM Battery

Glen, I have recently installed two of the Blue Seas ARC's--Had not thought of them as a voltage limiting unit for bilge pumps--but one potential problem could be the current draw: 12 ma in the rest mode and 175 ma in the sense mode (I have breakers before the ARC's, so that is not an issue for me--plus I am on battery chargers) However Abysmal wants low self discharge batteries, because he leaves the boat for long times.

Incidently the self discharge of an AGM is 1-3% a month, so there is potential of 35% discharge during a year--still not to the point that a battery is unusable, but not the best for it. If you leave even an AGM battery in a chonically low discharged state it will shorten its life. Also the AGM needs to be fully charged each time to achieve its best life span. Many regulators do not allow 100% recharge. So AGM batteries are not perfect and they do not fit all needs.
Old 09-03-2006, 10:28 PM
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Default Re: Killing an AGM Battery

thataway - 9/3/2006 11:25 PM

Glen, I have recently installed two of the Blue Seas ARC's--Had not thought of them as a voltage limiting unit for bilge pumps--but one potential problem could be the current draw: 12 ma in the rest mode and 175 ma in the sense mode (I have breakers before the ARC's, so that is not an issue for me--plus I am on battery chargers) However Abysmal wants low self discharge batteries, because he leaves the boat for long times.

Incidently the self discharge of an AGM is 1-3% a month, so there is potential of 35% discharge during a year--still not to the point that a battery is unusable, but not the best for it. If you leave even an AGM battery in a chonically low discharged state it will shorten its life. Also the AGM needs to be fully charged each time to achieve its best life span. Many regulators do not allow 100% recharge. So AGM batteries are not perfect and they do not fit all needs.
bob - good info and insight....thanks
Old 09-04-2006, 12:50 PM
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Default RE: Killing an AGM Battery

I'm not an expert on AGMs but have been replacing wet and deep cell batteries systems in my job for 20 years. Those batteries if continually not charged to a full state by a battery charger designed for either wet or gel cells will hit a ceiling under 12.7vdc full charge state. To over come this lower voltage ceiling we purposely discharge the wet cell battery to as low as possible before recharging. Sometimes it comes back to full charge but most times not and has to be replaced. If you do not want your batteries life to be decreased, I'd suggest a battery charger designed for the characteristics of a AGM.

As for the bilge pump, Westmarine sells an automatic bilge pump switch with a spring loaded switch for the manual mode.

HH
Old 09-04-2006, 01:05 PM
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Default Re: Killing an AGM Battery

all currnent AGM's need no special treatment or special chargers. they charge just like std flooded batts. Do a search here for confirmation...it's been discussed may times with supporting documention....
Old 09-05-2006, 05:50 AM
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Default Re: Killing an AGM Battery

Thanks for all the information. Looks like an onboard charger is the ticket for battery life and a reliable start.
Old 09-05-2006, 11:42 PM
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Default Re: Killing an AGM Battery

Glen,
What battery charger would you suggest? I have 2 Optima blue tops: D31 &D34.

Thanks,

Doug
Old 09-06-2006, 01:41 AM
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Default Re: Killing an AGM Battery

I agree with Glen E, that AGM batteries can be handled by a "normal" 3 stage lead acid battery charger. The charger I chose is the Prosine True charge 20 amp. (there is also a 40 amp)--this would be a good choice for the Optima batteries. The Prosine has an AGM setting--with slightly higher Bulk charge and slightly higher float charge, as swell as a temperature compensation--which does make quite a bit of difference in the charging of batteries. Also this charger will assure that the batteries are taken up to full capacity.

There is also the issue of equalzing sealed recombant batteries---there is a risk doing this---and I would not suggest it, although some companies have said it is "OK"--sealed batteries have been known to explode, or at least crack the case with prolonged higher voltate--even 15.5 volts.

One of the best and comprehensive articles on AGM's is by Steve Antonio called the ABC's of AGM's. Certainly a worthwhile read. There are others who say that AGM's have to be treated like Gel Cells--in my experience that would be a mistake, and would lead to chronically undercharging the batteries.

Incidently I don't like to leave chargers on all of the time. I often will set a timer to come on xx hours a day, or XX hours every other or every 3rd day...

One can also maintain batteries with solar pannels--and if the boat is stored outside, this is not a bad way to go--you don't need a large solar pannel.
Old 09-06-2006, 07:04 AM
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Default Re: Killing an AGM Battery

Fishin Spot - 9/6/2006 12:42 AM

Glen,
What battery charger would you suggest? I have 2 Optima blue tops: D31 &D34.

Thanks,

Doug
I use a Promariner - going on 2 years - no problems and mine is on 24/7 whenever the boat is not being used...

http://www.promariner.com/productFea...oductNum=51030

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