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Author Topic:   Starting Battery for Mercury OptiMax
dcritch posted 04-24-2006 06:45 PM ET (US)   Profile for dcritch   Send Email to dcritch  
I would like to use a dual purpose battery for my 170 Montauk however my 90 Optimax owners manual says in big bold print that I can only use a cranking battery with 800cca and 1000ca. They go on to say basically no deep cycle batteries allowed. I would like a dual purpose battery because my gps sounder,vhf, and electric downriggers (I troll with the Optimax)are all connected to my starting battery. I keep the 170 on a bouy so my engine needs to charge the battery. I'm wired for dual batteries but according to the manual they both would have to be cranking batteries.

My question is this: Optima is now advertising The Optima dual purpose D900M as solving the starting requirements of the new Optimax outboards and still providing house service deep cycle ability. I called the Mercury help line and the call center person said they did'nt know anything about the Optima battery and repeated basically what the Optimax owners manual says about batteries. I called Optima and was told that the D900m was routinely used with Optimax engines

Are any Optimax owners familiar with this battery and better yet, is anyone using one as their starting battery?

glen e posted 04-24-2006 06:54 PM ET (US)     Profile for glen e  Send Email to glen e     
Buy an AGM battery from It is perfect for [a starting battery for the Mercury OptiMax outboard] and big V6 outboards. Ad cheaper, too. I own four for my big heavy-electrical-sucking Verado outboard motors.
dcritch posted 04-26-2006 06:56 PM ET (US)     Profile for dcritch  Send Email to dcritch     
glen e
Thanks for the information. The Cabela-brand AGM cranking/deep-cycle battery exceeds the Interstate-brand [conventional wet cell lead acid] cranking battery in every catagory.

[Marine] Cranking ampere ratings are 1195 vs 1000
Cold cranking ampere ratings are 945 vs 800
Reserve capacity is 178 vs 135 [of some undefined unit of measurement]

Why not use the dual-purpose AGM battery with the OptiMax? Do I have to be concerned with cranking ampere ratings in excess of the 800-CCA and 1000-MCA recommended by Mercury? Is there something about a deep cycle battery which could damage the OptiMax even though the [ratings] are high enough?

I really appreciate any guidence here because I'm not getting any useful input from Mercury or the Whaler dealer.

glen e posted 04-26-2006 07:00 PM ET (US)     Profile for glen e  Send Email to glen e     
The Cabella's-brand Group-24 size AGM battery will work fine with the Mercury OptiMax. It exceeds [the required specifications] for an[OptiMax] in every category
jimh posted 04-26-2006 07:26 PM ET (US)     Profile for jimh  Send Email to jimh     
The high rating for a starting battery for some motors, like the Mercury OptiMax, is required because the motor has extensive electrical drain during starting and is controlled by microprocessors which need a certain minimum voltage present to operate correctly. The OptiMax is especially sensitive to the voltage present because it has a double load of fuel injectors. There are two injectors for each OptiMax cylinder; one injector for the fuel and one for the air. These injectors are electrically operated. Thus the electrical load is quite high on these motors.

Mercury specifies a very high rating for the starting battery in order to minimize the potential (pun intended) for having low-voltage during start-up. A low voltage condition is going to be bad for the microprocessor, and it may inhibit starting, even though the engine is being cranked over.

The engine cannot tell what is supplying the starting current. It could be a really big dry-cell battery--the engine wouldn't know. As long as the battery can supply the required starting current, it will be able to start the engine.

Getting a battery of that required rating using a deep-cycle battery or an AGM battery may be more expensive than using a conventional wet-cell lead acid battery. Generally they provide the most current for starting for the least cost.

jimh posted 04-26-2006 07:30 PM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the prohibition against using a deep-cycle battery for a starting battery for a Mercury OptiMax, I speculate this is due to a fear that a deep-cycle battery will be used which does not have a proper rating. I don't think you will harm the motor if you use a deep-cycle battery that has the proper rating. Of course, you have to keep it fully charged to get that rating; it won't meet specifications if it only has 20-percent charge in it.
Bthom posted 04-27-2006 01:11 AM ET (US)     Profile for Bthom  Send Email to Bthom     
I will be that guinea pig within the week.
I have two new expensive deep cycle batteries I bought before I was compelled to replace my motors with new 150 H.P. Optimax's.
These batteries have the required amperage ratings cited in the Mercury literature, but are still deep cycle batteries, and I am certainly going to try them before I replace them. They will jump start my diesel pickup which has a compression ratio of 21.5 to 1, so I will be really surprised if they prove inadeqate for the outboards.
If need be I can always parallel them up if I have trouble getting started. I'll let you know how it works out.
dcritch posted 04-27-2006 02:53 PM ET (US)     Profile for dcritch  Send Email to dcritch     
glen e and jimh
Thanks for the help. I'm going to go ahead and order a couple AGM batteries from Cabelas.

Let me know things work out with your new engines. I should be back in the water in a couple weeks and I'll let you know how things go.

Can anyone recommend a good marine towing company in the Puget Sound area?

dcritch posted 09-05-2006 03:49 PM ET (US)     Profile for dcritch  Send Email to dcritch     
glen e

Thanks again for the cabelas AGM battery suggestion.

I've been starting my Optimax, running my electronics, and operating my Scotty electric downriggers all summer without any problem. I have'nt even switched over to battery 2. Only observation of any note is a slight change in pitch of engine noise when trolling with Optimax at dead slow and raising both downrrigers at same time using 12 lb cannonballs.

Engine always starts instantly.


davej14 posted 09-05-2006 09:26 PM ET (US)     Profile for davej14  Send Email to davej14     
A starting battery is constructed with relatively thin high surface area plates and is NOT designed for running significant electronic loads without the motor's charging system. With a small number of partial discharge cycles a starting battery will be damaged and lose capacity. For a motor that requires high starting current this could be a bad thing.

AGM does not specify the purpose for which the battery is designed, it just specifies the way that the electrolyte is constrained.

A dual purpose battery with adequate CCA, like the new Optima blue top, is the way to go. Two batteries would be even better.

dcritch posted 09-06-2006 12:13 PM ET (US)     Profile for dcritch  Send Email to dcritch     

The Cabelas AGM batterys (I have two) are represented as "completely maintenance-free batteries also serve double-duty on the water, serving as either a cranking battery or a deep-cycle power source." They also exceed both the cranking and cold cranking (800/1000) requirements of mercury.

I'm not an authority on the different batteries out there but the Cabelas was the only group 24 battery which exceeded both cranking and cold cranking amp requirements. I looked at the Ultima (which specifically states its Optimax friendly) but the Amp rating was less than what Mercury recommended for my 90 Optimax. So far I,ve been very impressed with the batteries but always appreciate any input.

These are also a very compact batterys which can be situated in my center console so I actually have more room than I did with the single factory battery which required the big bulky battery box.

davej14 posted 09-06-2006 08:48 PM ET (US)     Profile for davej14  Send Email to davej14     
After checking the Cabelas' website I see what you mean. Although the Optima D31M also exceeds the specifications for your Optimax, the Cabela's AGM does also at a lower price and in a smaller package. When my Optima fails I think I will try one of the AGMs from Cabelas myself.
jimh posted 09-06-2006 08:53 PM ET (US)     Profile for jimh  Send Email to jimh     
More discussion on the Cabela's AGM Battery:

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