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Author Topic:   Charging Absorbent Glass Mat Battery From Outboard
DANO posted 08-14-2006 06:05 PM ET (US)   Profile for DANO   Send Email to DANO  
[Implied question: What is the voltage output of a 2005 Mercury Classic 60-HP motor's alternator or battery charging system?]

In a never ending search for weight reduction, I have purchased a [small absorbent glass mat] (AGM) battery to run nothing more than the running lights and instrument lights on my project 13-foot Boston Whaler boat. I know [that an AGM battery must be] charged at a lower voltage than standard wet cells.

Do you think setting the battery on a trickle charge with the appropriate charger while the boat is out of the water should keep me out trouble?

Is the alternator going to fry the little u-1 sized battery?

I can still bring it back if it is unused. Any help would be appreciated. Thanks. dano

sosmerc posted 08-14-2006 11:46 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
The 2005 classic 60 does have a combination regulator/rectifier and should keep the voltage near 14.5 volts, but it is my understanding that both AGM and GEL batteries do not get along well with outboard alternator-driven ignition systems. Mercury recommends standard flooded starting batteries for all their outboards. Mercury outboards that have a belt driven automotive style alternator seem to work fine with both the Orbital and the Optima batteries, though Merc still recommends a 1000 MCA starting battery in all Optimax engines.

That classic 60-HP should do just fine with a standard group 24 starting battery of only 550 MCA. West Marine has one that only weighs 34 lbs, which isn't too bad.

jimh posted 08-15-2006 08:45 AM ET (US)     Profile for jimh  Send Email to jimh     
[Moved this discussion of a small boat's electrical system to the discussion area whose focus is small boat electrical systems.]
jimh posted 08-15-2006 08:47 AM ET (US)     Profile for jimh  Send Email to jimh     
I was completely unaware that an absorbent glass mat battery could not be charged by the charging system of an outboard motor. These types of batteries are being sold all the time for use with outboard motors. What is the source of the information regarding absorbent glass mat batteries being incompatible with outboard charging systems?
jimh posted 08-15-2006 09:05 AM ET (US)     Profile for jimh  Send Email to jimh     
[Fixed typo in my revised TOPIC line. Was "Charing Absorbent Glass Mat Battery..." Perhaps a Freudian slip--jimh.]
DANO posted 08-15-2006 05:10 PM ET (US)     Profile for DANO  Send Email to DANO     
From what I have gathered, gell [batteries] [should be] charge[d] at a lower voltage (14.1 max.) than other [batteries]. I misspoke when I previously said AGM. (Apology extended.) I was just concerned with the fact that most charging systems will charge at 14.5 volts on [average]. Does this mean that I will fry the [battery] or will it just not take a charge? Hence the thought of an applicable charger during trailer time.
jimh posted 08-15-2006 08:10 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the clarification regarding the distinctive characteristics of gell batteries which make them somewhat problematic to charge with an outboard motor, while absorbed glass mat batteries use the same chemistry as wet-cell lead acid batteries and seem to be perfectly suited for use in a small boat and to be charged by a regulated outboard motor charging circuit. I am glad to have that made clear.

I do not know what the average voltage output of most charging systems is, but I think that something above 13.2-volts is needed. Generally the larger the current capacity of the charger system the higher the voltage output might tend to be, or at least the more stiffly regulated it will be as the output current load increases. But a battery just absorbs the current it can, and if you connect a nearly fully charged battery to a motor that can deliver up to 70-amperes of charge, you will not suddenly be pushing 70-amperes into the battery.

I would not be afraid to let the AGM battery be charged by your outboard motor (which I assume has a regulated charging output). It ought to charge it satisfactorily. It might be advisable to have the option to switch the battery out of the circuit once it is charged. But many boaters use AGM batteries exclusively and do not seem to be reporting problems as a result of charging them with their outboard motors.

DANO posted 08-15-2006 08:35 PM ET (US)     Profile for DANO  Send Email to DANO     
THANKS JIM...I'll keep you posted whenI splash her....
aja posted 08-25-2006 10:54 AM ET (US)     Profile for aja  Send Email to aja     
I had heard of differences in charging between flooded cell and AGM batteries, but was under the impression that either type would work fine by themselves in a standard charging circuit. The problem I had been told of was having a combination of both in a bank and trying to charge them together.
Mister S posted 08-25-2006 11:38 AM ET (US)     Profile for Mister S    
I just replaced my AGM's w/ lead acid starting batteries. I cannot state directly that the AGMs caused problems but my mechanic and others will tell you that Mercury recommends that only lead acid batteries are used. Just replaced stator and both regulators, not willing to risk doing it again. $$$ See other post 200 Merc charging problems.
DANO posted 08-25-2006 06:36 PM ET (US)     Profile for DANO  Send Email to DANO     
Mister S,
was this a slow, evolving process or a sudden break down of your system? I'm still in the process of wiring, rigging, and so on and I don't want to destroy my 05 merc. 60 classic. I also read that merc. "RECOMMENDS" a flooded cell type, but let's face it, if we followed every manufactures recommendation we would still be unaware of the true fun of boating due to never getting on a "dangerous and unstable" plane....


Mister S posted 08-26-2006 04:51 PM ET (US)     Profile for Mister S    
I installed 2 AGM's and 2 new regulator / rectifiers in June. About 6 weeks later I had the problem, can't say it was caused by the batteries sudden or not. Is the cost of a stator + worth using something other than lead acid? If so I have 2 new AGM's for sale @$100 ea.
davej14 posted 08-26-2006 09:11 PM ET (US)     Profile for davej14  Send Email to davej14     
I question the concern about using AGM batteries. They have the same charging voltage requirements as a flooded cell battery (14.4-14.8 Volts). If you were charging them at 17+ volts there was something wrong with your charging system. You will clearly damage either an AGM or a flooded cell battery in a short period of time by charging at 17 volts.

If there is a factual explanation of why AGM cells should not be used with certain engines/charging systems I would like to have it explained.

Mister S posted 08-27-2006 03:24 PM ET (US)     Profile for Mister S    
So would I. I thought I had the ideal set up w/ 2 new AGMs. Like I said, I don't know that the batteries did or could cause a problem, just that Mercury recommends traditional batteries and I'm taking that conservative approach.
DANO posted 08-30-2006 05:26 PM ET (US)     Profile for DANO  Send Email to DANO     
What do you know of gell batteries and thier charging requirements? It seems like alot of conflicting facts surrounding gell and AGM batteries. the most (not necessarily the best perhaps) info I have found has been in the Boat US or West catalog...any info YOU may have would be greatly appreciated as I am always seeking knowledge of areas I am not proficient in....
davej14 posted 08-30-2006 09:18 PM ET (US)     Profile for davej14  Send Email to davej14     
A flooded cell battery and an AGM battery are both designed for charging at the same voltage (14.4V to 14.8V). Most charging circuits are designed for this. Gel Cells are designed for charging at a lower voltage (13.8V-14.1V) so if they are continuously connected to a "standard" charging system they will be overcharged all the time.

While doing some research I determined that the very high charge acceptance rate for AGM and Gel Cells could be the cause of potential alternator failures. They could overheat an undersized alternator if they were deeply discharged whereas a flooded cell will accept a charge at a much lower rate.

All things considered, I have been using an AGM cell with my 2000 Merc 75 2-stroke and would not go back to a flooded cell. I have much better resistance to shock and vibration, no possibility of electrolyte spillage, no need to check electrolyte fluid levels, no corrosive out-gassing in the console and I don't need to charge it in the Spring after storage. My personal favorite is the Optima brand Blue Top.

DANO posted 09-02-2006 01:47 AM ET (US)     Profile for DANO  Send Email to DANO     
sounds like I might want to consider taking my gell cell back and exchanging it for an A.G.M..... same size to fit in my U-1 boxwithout the associated heartburn worrying about frying my altenator or overcharging the finicky little battery...

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