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Author Topic:   AGM battery use with Mercury outboard
bigjohn1 posted 02-04-2007 08:02 PM ET (US)   Profile for bigjohn1   Send Email to bigjohn1  
In December 2005 I installed an Optima group 34 AGM battery in my MONTAUK 170 with Mercury 115 EFI. Since I load test my batteries on an annual basis out of habit, this one-year-old battery was just tested. The guys at NAPA used two different testers for confirmation and both said the battery was bad. Several subsequent tests said the cold craking amps were at less than 400. Since the battery came with an 18-month free replacement warranty, they gave me a new battery free of charge.

This experience seems to agree with what some here have said regarding Mercury recommending the use of flooded cell batteries. I presume the high rate of charge on my outboard is somehow damaging the battery at an accelerated rate.

bluewaterpirate posted 02-04-2007 08:20 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
BigJim ...... been using group 24 AGM's for 2 years and no problems whatsoever.
bigjohn1 posted 02-05-2007 12:41 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Tom, I do not recall what size outboard(s) you have on your boat. I seem to recall this being an issue moreso with mid-range Mercury models but I may be wrong on that.
bluewaterpirate posted 02-05-2007 08:53 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
2002 225 Opti ......
davej14 posted 02-05-2007 10:37 AM ET (US)     Profile for davej14  Send Email to davej14     
Which Optima group 34 battery are you using? The 34M is a starting battery. If you use it to power electronics without the engine running you will damage the battery in a relatively few discharge cycles. The D34M is a dual purpose battery and is designed for multiple discharge cycles. A properly selected AGM battery should work in your application.
bigjohn1 posted 02-08-2007 09:10 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
davej14, no electronics are running when the outboard is shut off. I am an ocean troller so this is not an issue with me but your point is well taken. The battery is an Optima blue top. I am going to hook a meter to the battery with the engine running to check the operation of my stator and rectifier/regulator.
davej14 posted 02-09-2007 11:11 PM ET (US)     Profile for davej14  Send Email to davej14     
That was going to be my next suggestion. Let us know what you find out.
bigjohn1 posted 02-10-2007 04:54 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Conducted a battery test at the terminals with engine running. I used an accurate Fluke meter so I trust the value it gave: 14.5 volts. The book says the charging system is fine and of course since the battery is brand new, it is also fine. The question still remains though, what fried my original Optima blue top in 13 months use?

As has been stated in this forum numerous times by Jim and many others, it seems Mercury mid-range outboards charge at very high values. I think this is causing my batteries not to last as long. The engine is 2.5 years old and I am already on battery number three.

jimh posted 02-10-2007 11:02 PM ET (US)     Profile for jimh  Send Email to jimh     
An absorbent glass mat (AGM) battery is a valve-regulated lead-acid (VRLA) battery. According to one paper,

"It has long been common knowledge that VRLA batteries lose capacity much earlier in their life than their flooded counterpart."

I know there is a certain infatuation with VRLA AGM batteries among some recreational boaters. They are lighter in weight than conventional flooded cell lead-acid batteries. They are often smaller in size in some cases. They cannot spill (because they are sealed). The VRLA AGM may be more rugged and able to withstand vibration and harsh motion better than a flooded cell lead-acid. Those are all good qualities. However, it appears that they are not likely to have a longer life span.

As for the characteristics of the alternator output of a 115-HP Mercury EFI motor, I really am not familiar with them. Regarding Mercury outboards and batteries, about the only well-known characteristic I am aware of is the need for certain motors to have rather substantial cranking current capacity for proper operation.

My recollection of your motor is that it is a four-stroke engine with a power head made by Yamaha. I don't know if the charging system on that motor is a Yamaha design or a Mercury design. If the motor's charging output is regulated at 14.5-volts it sounds like it is working properly.

The life span of a battery is often related to the number of charge/discharge cycles, as well as the depth of the discharge cycles. The more charge/discharge cycles and the greater the depth of the discharge, the shorter the life of the battery. In your installation this may be a greater influence than the characteristics of the charging current.

My local battery specialty store dealer told me not long ago that Optima batteries have recently undergone significant price increases which may be due in part to very heavy demand for them for use in U.S. military vehicles.

In your case, the replacement cost is zero, and, since you had already removed the battery for testing, there really is no extra burden on you to install the free replacement.

Does the warranty period of the battery re-start at zero with the new battery? Or does this battery resume the original battery's life cycle, and you are now 1.5-years into its life span?

bigjohn1 posted 02-15-2007 08:53 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Jim, Thanks for the info and the point toward a great battery resource. Regarding your question on my warranty, it is 18-month free replacement and then pro-rated for an additional 18 months. Since my battery was replaced, it's warranty does not reset back to zero, the new battery gets (in my case) 5 more months of free replacement protection and then it goes into the prorated pahse of the warranty period.

I recall that my first battery which came with the boat at delivery was a flooded Interstate deep cycle marine. I had to add water to this battery about every 50 hours or so of engine operation. Right or wrong, I chock this up to Mercury's charging system charging at such a high rate. Adding water to a console-mounted battery can be a real pain given I must unload the console and remove the battery. For this reason, I figured the AGM wqould be the natural right choice. I guess the jury is still out on this.

Mambo Minnow posted 02-17-2007 08:17 PM ET (US)     Profile for Mambo Minnow    
Bluewater, I have same hull as your Ventura 21, but the Conquest. How do you get your portside battery out?

The euro transom makes that a PITA! I have the starboard battery out no problem, but it looks like disconnecting the cables on the port side one and taking it out through the removable hatch in the centreline transom well (directly in front of the motor) is going to require much contortion!

If you have any tricks to making that task easier, I'd sure appreciate it. Read your other posts recommending the Optima or Cabela's AGMs. Might go to those next if it requires less times removing the batteries. I now truly appreciate the battery set up on the new Conquest 345.

bluewaterpirate posted 02-17-2007 11:13 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
My batteries are forward in the helm console on the starboard side of the boat. I have easy access to them and my battery switches. 12095709/file.jpg 12492497/file.jpg


Mambo Minnow posted 02-17-2007 11:35 PM ET (US)     Profile for Mambo Minnow    
Thanks Master Chief! You have a beautiful neat installation. I like your battery charger and fuse block upgrades. Unfortunately, my cabin model has the batteries aft under the transom. Much more difficult access.

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