I have 120hp Force by Mercury, what size cranking amps battery should I get also I have seperate battery for my trolling motor, but console electronics are hooked up to my cranking battery. Should I go with a dual purpose battery?

Get a 1000 amp. cranking battery and you should be fine.

I really do`nt see the need for an expensive battery on this set up unless he is running 2 big lowrance or humminbird units.

At this point I don't even have a depth finder, but when I do it will be 1 small unit.

FROM MERC'S WEBSITE:

What is the correct battery for the outboard motor?
Note: These are minimum engine specifications. Additional electrical loads from the boat will require larger batteries.


2-Stroke Models


75 - 125
525 Marine Cranking Amps MCA) or 450 Cold Cranking Amps (CCA)
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Any battery you buy with bigger cranking amps than Mercury itself recommends is just money and weight wasted.

You though also do want to buy as big of Reserve Minutes (RM) in this battery as you can afford if you want to run many electronics.

Those are amps for a fully charged battery. As the battery discharges it loses some of its ability to supply a full load.

A battery rated higher than the minimum will give the required amps longer as the battery discharges during a day and also as the battery ages.

I'll say it once more. A 1000 amp. batt. is the way to go. The more amps. the better. NO Question. If you have a situation where the motor is hard to start or you do a lot of starting or the charging system is not re charging the battery back to full capicity the more amps the less likly you will be stranded. Plus they also last longer and don't cost that much more. Mercury offers the minimum just to get it started and operating. It's just that a minimum. Going up in amps is not a waste...

Quote: (Plus they also last longer and don't cost that much more) ARE YOU KIDDING? I can buy 2 700-750cca batteries for what 1 good 1000cca cost. Never heard that a higher cca battery will last longer. They last longer because they are a better brand like Optima, Decca, Delco Voyagers ect.

Interstate 1000 amp cranking, free 1 year replacement, $89.99, no core charge. Strong enough to weld with.

Best buy I have found is go to walmart and get one of the big everstart max dual pupose deepcycle batteries, they last a long time have a 3 year free replacement, and like gary said you wont regret having more than enough battery.

matt

It seems there is a inherent feeling that somehow buying a battery with more cranking amps (CCAs)than what is really needed by the motor will somehow be able to supply more motor starts especially later in the day (as if your alternator went out for example).

That would be true if batteries(of a given case size) were always constructed such that the more peak rated cranking amp (CCAs) capability we paid for also still actually corresponded to the same spare stored spare cranking amps. But they are not made like as only so much lead can fit into the battery case .

High CCA batteries can really deliver a punch turning over a big engine, but they still have to fit in the battery case size and so will tend to have lousy spare capacity. A proper sized CCA cranking battery though will have plenty of amps to turn the smaller engine and it will tend to have room in its case for lead giving it lots of spare capacity.

For the cost of the lead in the 1000CCA battery mentioned above , a manufacturer could mold it and make conceivably it into a 2000 CCA rated battery but it would only crank an engine (small or large) only a few times before being terribly discharged. So a 2000CCA battery could still work out quite poorly on a motor like the above needing only 450CCAs.

Extra unneeded CCAs just don't translate automatically to more starts. And increasingly , we are needing that precious spare lead in a cranking battery to be devoted not to cranking but to reserve minutes to keep our electronics supplied.