TOPIC: AGM & Optima Battery - Opinions?

Hey all,

For a '62 Merc 1000 or any in line 6 , the only spec I have seen for the battery is to have a minimum of 70Ah. I'm going to mount my battery forward for ease of access to the master switch and to move some weight forward. This could be a potentially "rougher" location with more vibration so I am considering an AGM battery.

What are your thoughts, experience on AGM's and has anyone used the cylinder style Optima brand? They have 3 dual use models:
D34M is 55Ah, CCA is 750
D27M is 66Ah, CCA is 800
D31M is 75Ah, CCA is 900
www.optimabatteries.com/products/bluetop

Then there are other brands of AGM with the traditional rectangular case.

For those of you running a classic 6 cylinder Merc, what are your battery specs, brand, etc?

Thank you,
Eric

AGM and Gel Batteries are excellent batteries but as with just about everything they have their pros and cons. The pros are they last a lot longer than lead acid wet cells, and you never have to replace the fluid in them. The con is, to last that long, correct battery charging is vital. The typical alternator on an older outboard motor or inboard will ruin an AGM or Gel in a very short period of time. Both are very sensitive to charging voltage and battery temperature. They must be charged with a "smart" charger that senses their current charge state and the temperature of the battery. The charger must also be at least a 3 stage, preferably a 4 stage charger. Most alternators on old engines just dump a lot of amps into the battery. That's ok for lead/acid wet cells, but it will quickly dry out the electrolyte in AGMs and Gels. Before you buy one read up on it. Start here newboatbuilders.com/pages/electricity3.html

Good Morning Ike and thank you for the reply and link. Yes, I got a little input from the Merc facebook group as well and in addition to the charging sensitivity, comments stated that a voltage regulator would be needed so that the vintage alternator is not overworked and eventually fail. Sounds like I should stick with the standard lead acid type. Maybe a little vibration dampening as I would like to mount it towards the front, centered under the dash? Starting to frame up the box now. Picture attached. Cup holders on in the little shelf, light switches on upper slant, fuse box on back of vertical board and master on off on the driver side exterior. I have some thick closed cell rubber foam that I can mount under and around the base of the battery box once the sides are on.
again, thx & Happy Holidays-
Eric

As long as the battery is in a well ventilated space (they give off hydrogen gas when charging) and easily accessible so you can check the fluid levels, should be ok. The battery boxes are good. They contain any spilled electrolyte and make it easier to anchor the battery. Batteries need to be fastened down so they won't move if the boat is bouncing or rocking around. Looks good.

yes, there will be plenty of open space around the box under the dash. sides are now on and sprayed with Zolatone. I've got some left over closed cell foam that will go in the bottom to dampen vibration and I'll put footman's loops on the raised inner rim for the strap. I'll have additional pics under the '64 custom craft "member projects" thread when I get the cup holders and switches mounted on the face.

Thanks again for your incite !

For any Mercury inline-6 2 stroke, 9 AMP charging system, I strongly recommend an Interstate 1000 CCA Marine Cranking Battery.
To use extended battery cables,...Be sure and use a minimum 4 AWG stranded copper.
I also strongly recommend replacing the original rectifier with a Mercury (6) wire regulator with a built-in rectifier to control voltage output , which aid in the longevity of your ignition system.
Mercury part number 883072T, 8M0084173. or CDI-e #194-5279
All are very expensive new, but used ones are always on eBay for a fraction of the cost, and they rarely fail.
Mercury charging systems are confirmed to not work well with Deep Cycle or gel-cell batteries.
doc,...Keeping Mercs alive since 1965

Morning Doc,

All great info ! Thank you for the battery recommendation and confirming the larger cables.

I'll keep an eye out for a 6 wire regulator as suggested. If any one has one to sell, please let me know-

Again, I appreciate your assistance,
Eric