BATTERY QUESTION

[TRRANGER]

After making the mistake of installing the wrong type of battery AGM on an 87 Mercury 175 and having an electrical fire and a shorted out rectifier I am looking at finding out what battery is supposed to be the cranking battery for a 2009 Mercury Optimax 2 Stroke 250.  Is an AGM ok or should it be a Lead Acid. It is currently a group 31 lead acid marine cranking battery by interstate, I have only recently purchased this boat so I am looking to not hurt anything. 

[snagged in outlet 3]

@fishinwrench

[jdmidwest]

AGM stands for a fiberglass mat that stands up to more vibration stress than lead plates.  They still output the same voltage, but have different chargers and charge ratios.

But, I will let the Fishinwrench chime in.  They may affect boat electronics differently based on engine designs..

[fishinwrench]

#1.   The AGM battery is NOT what caused your electrical fire.   If it was a Voltage Regulator meltdown then THAT was more than likely caused by YOU 😅   (trying to get ONE MORE SEASON out of a dying battery.....or failing to maintain a good connection to the battery).    If a V6 outboard loses it's connection to the battery....even for 2 seconds.....then you just fried the diodes in the voltage regulator, and probably the tachometer, and unless you constantly are monitoring a voltmeter you'll never know. 

 

900+ cranking amps is what you need, regardless of where it comes from.   Keep your battery fresh....and keep those terminals TIGHT & CLEAN.    Replace your cranking battery every 3rd year, whether you think it needs it or not.   

And float-test any WING NUTS before using them for your primary battery connection.    Toss them in the lake, and if they float then you can use them.   Replace them with 1/2"-9/16" nuts and tighten them with a wrench 👍

[Maverickpro201]

And float-test any WING NUTS before using them for your primary battery connection.    Toss them in the lake, and if they float then you can use them.   Replace them with 1/2"-9/16" nuts and tighten them with a wrench.

I have always found that the wing-nuts are trash. They never float for me. So I always use nuts.

[jdmidwest]

11 hours ago, Maverickpro201 said:

And float-test any WING NUTS before using them for your primary battery connection.    Toss them in the lake, and if they float then you can use them.   Replace them with 1/2"-9/16" nuts and tighten them with a wrench.

I have always found that the wing-nuts are trash. They never float for me. So I always use nuts.

My wing nuts always come with the little rubber protectors that trap air, and they are made out of light weight pot metal.  They will float.

But my hands are weak and a wrench and a hex nut works better.

[Terrierman]

I recently learned that newer model cars and trucks have AGM batteries.  Wife has a 2018 Jeep Renegade that recently had a bad battery.  It caused all kinds of mystery problems.  Sun Roof, Key Fob, Transmission shift points, all kinds of codes.  New battery fixed them all, after resetting the computer by disconnecting battery with engine running.

[tjm]

AGM batteries ain't a new thing, they came out back in the late 1970s or maybe ~'80, and the first brand (can't recall which)  to be widely marketed was not very good, about a 65% return according to the parts store guy that I talked to. One distributor ended up getting the warranty returns from lots of sellers and I counted 7 pallet loads of bad batteries a few months into the sales campaign. They got better with time and are pretty good now. I think GM cars all came new with them since the mid '80s.