Which Battery

Dear Forum, I own a 1988 Mercury 90hp 2 cycle 3 cylinder outboard. The serial number is: 0B302485. My question is what size battery would you recommend for this boat being that it has no voltage regulator other than a rectifier and battery to regulate charge voltage. I seen somewhere that using a battery with a MCA of over 700 is preferred for this unregulated system? Can someone give me a push in the right direction on which battery is best for my setup? Thanks.

with a rectifier only system you do not want to use a maintenance free or a gel battery..the rectifier will eventually blow using these batteries....you want the kind that you have to check and occasionally add water....

700 is fine..i would not go any higher than that...

the key to all battery and charging system life id to have the battery fully charged when you put the boat in the water..let the charging systm maintain a battery charge instead of drawing a lot of current and charging a down battery...and make sure all connections are clean and tight...throw the wing nuts that come with the battery away and get regular hex nuts..

I have rectifier charge systems on all of my motors save one.

I'm also a pretty cheap &*&(*((.

Walmart carries a group 24 Marine starting battery that is about the cheapest "marine" battery I have found on the market (at least on my side of the border). It's a heavy plate, lead acid battery well suited to rectifier systems.

They tend to last me 4 to 5 years under somewhat extreme conditions - 90 degrees in the summer, -20 in the winter with the battery sitting in an unheated garage (albeit connected to a "smart" trickle charger).

Batteries are rated a couple of different ways to further confuse things.

A battery that has 500'ish CCA (cold cranking amps @ 0 degrees) would have a rating of 600 MCA (marine cranking amps @ 32 degrees) or 750 cranking amps @ 80 degrees.

Since most of us only boat at temps above the freezing point of water, whichever battery you choose will always produce more amps than it's rating.

And for your particular model, the higher authority (Merc service manual) states it needs a minimum of 350 CCA with 100 minutes of reserve - which is about 450 MCA.

The battery I use from Walley World is the EverStart Lead Acid group 24-DC rated at 690 MCA (was made by Exide before they went bankrupt, don't know the actual mfg anymore - East Penn would be my guess) - more than enough