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Author Topic:   AGM Battery: Survey of Mercury or Yamaha 90-HP EFI Four-cycle Outboard Engine Owners
howlingdogsteve posted 04-17-2012 09:42 PM ET (US)   Profile for howlingdogsteve   Send Email to howlingdogsteve  
Hi all--Has anybody had success running an AGM battery with a 2006 Mercury or Yamaha 90-HP EFI four-cycle outboard engines? Thanks much.--Steve
Teak Oil posted 04-17-2012 11:13 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
Not running a Mercury motor, but my rig has had an AGM and a standard battery in tandem with my Evinrude for many years without [malfunction].
ericflys posted 04-18-2012 04:57 AM ET (US)     Profile for ericflys  Send Email to ericflys     
I'm running two AGM physical size Group-30 batteries on my Outrage 18. I looked at many different brands, and their specifications. I'm by no means an expert on the subject but depending on battery size, the Sears DieHard Platnum (made by Odyssey) and the Cabela's AGM (with non-standard terminals, but will work with standard cables) seemed to have the best ratings.
jimh posted 04-20-2012 08:13 AM ET (US)     Profile for jimh  Send Email to jimh     
Absorbed glass mat (AGM) batteries are sealed lead-acid (SLA) batteries. An AGM battery, like any SLA battery should not be charged with voltages that will float the battery terminal voltage above [13.5-Volts], otherwise there is risk for the electrolyte to be boiled off, vented out, and lost. This is the only characteristic of an AGM battery that I can imagine would cause its suitability to be compromised for a specific 90-HP outboard engine.
TC Goldman posted 04-20-2012 09:50 AM ET (US)     Profile for TC Goldman  Send Email to TC Goldman     
2005 115hp Mercury EFI 4 stroke. AGM (2007) from Cabeles, not one problem. Charges just fine and I leave it in the boat all winter (Michigan).
I also have Sears AGM's on other boat , 2 years no problems (Verado 225 motors)
jimh posted 04-20-2012 08:52 PM ET (US)     Profile for jimh  Send Email to jimh     
What characteristic of the Mercury or Yamaha 90-HP EFI four-cycle outboard is suspected to make it particularly special or difficult to use with an SLA or AGM battery?
howlingdogsteve posted 04-20-2012 10:30 PM ET (US)     Profile for howlingdogsteve  Send Email to howlingdogsteve     
According to the service manual, peak voltage of the rectifier regulator output @ 1500 rpm (unloaded) is 14.8V and @3500 rpm (loaded) is 15.1V, hence the concern.
jimh posted 04-20-2012 10:48 PM ET (US)     Profile for jimh  Send Email to jimh     
Measure the voltage at the battery terminal to see if there is a problem. The voltage figures cited in the manual may be at the alternator output. It would be typical to have some voltage drop between the alternator's output and the battery terminals.

Also, when measuring a voltage with accuracy to a few tenths of a volt in a nominal 13.2-volt system you need a meter with a calibration accuracy of

0.1/13.2 = 0.7-percent

Most voltmeters owned by a boater are no more than 5-percent accurate. I think we are quibbling about a few tenths of a volt.

howlingdogsteve posted 04-21-2012 07:47 AM ET (US)     Profile for howlingdogsteve  Send Email to howlingdogsteve     
I will measure and report back. There has been anecdotal evidence both here and on other forums that these motors have high charging outputs which allegedly contributed to early battery failure.
jimh posted 04-21-2012 09:21 AM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the added information about the concern for the AGM battery use with this particular Mercury or Yamaha 90-HP outboard engine.

My remarks above about float voltage were not correct. According to several sources, for example , the maximum float voltage should be closer to 13.5-Volts for an AGM battery, not the voltage I mentioned earlier. If the Mercury and Yamaha engines under discussion routinely try to float the battery at 15.1-Volts, the optimum float voltage is being exceeded by more than 1.5-Volts. That could be a concern.

Measure the actual voltage at the battery terminals with your present battery. This should give you an approximation of what you will have with a new battery. The present battery may only approximate the new battery terminal voltage because a new AGM battery should and most likely will have a lower internal resistance. This will tend to hold down the terminal voltage compared to the present battery.

For several years I have been using a small float charger to maintain an AGM battery on my test bench. This charger is described as a "precision" float charger. I just checked the terminal voltage of the AGM battery that the precision float charger has been maintaining for several years. The terminal voltage as measured by my Fluke DMM was 13.2-Volts.

howlingdogsteve posted 04-22-2012 09:32 AM ET (US)     Profile for howlingdogsteve  Send Email to howlingdogsteve     
There seems to be little consensus amongst battery manufacturers.
Since Odyssey makes the AGM I'm interested in for Sears, I checked with them.

From the Odyssey Battery Technical Manual:
"The message to be taken from this graph is clear – in deep cycling applications it is important to have the charge voltage set at 14.4 – 15.0V. A nominal setting of 14.7V is a good choice, as shown by the test results...
If the voltage output from the charger is less than 14.2V or more than 15V for a 12V battery, then do not use the charger."

That puts the Mercury/Yamaha right on the edge voltage wise. As pointed out, there should be some voltage drop at the battery.
If the rain holds out here in East, I'll take real world measurements and report back.

jimh posted 04-22-2012 01:05 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is information from the manufacturer's label of two AGM batteries I have on my electronics bench:

Float charge voltage = 13.5 to 13.8 VDC at 77°F

Float charge voltage = 13.5 to 13.8 VDC at 77°F

howlingdogsteve posted 04-22-2012 01:26 PM ET (US)     Profile for howlingdogsteve  Send Email to howlingdogsteve     
The numbers I stated above are for absorption charge with optimal being 14.7V.
Odyssey states 13.5 - 13.8V for float (or maintenance charge) with optimal being 13.6V.
Remember the three charging stages are Bulk (brings a battery's voltage up to accept a charge), Absorption (the actual charge) and Float (maintenance charge).
Hope this clarifies the information.
jimh posted 04-22-2012 10:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Outboard engine alternator-based charging systems don't have phases. They just pump out current at a regulated voltage. The differential voltage between the battery terminal voltage and the alternator output determines the charging current, along with the battery's internal resistance.

An AGM battery may have a lower internal resistance, which helps the AGM battery promote higher charging current from the alternator.

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