Parallel battery specs

[YellowT]

Hello. I'm adding a second battery to a boat with an outboard (2022 Mercury 150 4S). The two batteries will be wired in parallel. The first battery came with the boat and outboard, all of which are six months old and have 30 hours of use. That battery - not my choice - is an Optima Blue Top marine dual purpose, AGM, D27M (group 27).

Here's the question. I understand that the battery I'm adding should have the same specs as the original battery - AGM, amp hours, cranking power, marine and dual purpose, etc. However, I've been told that the brand of battery should be the same and that this is especially true of Optima batteries because of their construction ("spiral technology" or something...). I'd prefer to go with a different brand, if possible (due to price and prior experience with Optima - however, I've had no problems with the Optima currently in the boat.)

Anyone have insight? Thanks.

 

[roscoe]

Buy 2 batteries of your choosing.
Then you will have what you want.

 

[tpenfield]

It might be better to buy 2 new batteries as suggested. Also, you will want to wire the batteries through a Perko switch, so they are not always connected together.

 

[silverbul]

Hello. I'm adding a second battery to a boat with an outboard (2022 Mercury 150 4S). The two batteries will be wired in parallel. The first battery came with the boat and outboard, all of which are six months old and have 30 hours of use. That battery - not my choice - is an Optima Blue Top marine dual purpose, AGM, D27M (group 27).

Here's the question. I understand that the battery I'm adding should have the same specs as the original battery - AGM, amp hours, cranking power, marine and dual purpose, etc. However, I've been told that the brand of battery should be the same and that this is especially true of Optima batteries because of their construction ("spiral technology" or something...). I'd prefer to go with a different brand, if possible (due to price and prior experience with Optima - however, I've had no problems with the Optima currently in the boat.)

Anyone have insight? Thanks.

just buy another battery with the same specs, no worrys, sounds like someone, Optima or other people with their buy the same are peeing on your leg and telling you its raining. as a mechanic for 50 years, im pretty sure about this, just not intuit sure. lol

​

JMO.

 

[stresspoint]

I'm no battery expert ,the battery's are going to be hooked up parallel so as long as they are both 12v all will be well .as the 12 v is still going to be 12v at the end of the line.

running in series is a whole other ball game.

 

[airshot]

A boat is not the best place for a fire or explosion, so why take that chance ??

 

[stresspoint]

A boat is not the best place for a fire or explosion, so why take that chance ??

why would you have a fire or explosion ?, just curious.

from my understanding , correct me if i am wrong , so long as both batteries are 12v , only the amperage could change if both battery's are different to one and other. ? would the alternator only charge and input what the battery's can take.
as i posted , I'm no expert on batteries , but i have jump started may times and never had explosion's , IE one flat battery with not enough amps to kick a motor and the other fully charged , the alternator eventually adds volts to the battery and builds it to a amperage the battery can hold ,no further.

 

[Lou C]

You can do it 2 ways:
one way is the typical #1, #2, 1+2 and off switch, 1+2 parallels the batteries, which should be used only if neither battery has enough amps to start the engine, or you want to charge one of the batteries which is weaker than the other, but do not leave it on 1+2 because then the weaker battery will suck amps out of the stronger one.
the other is to use an automatic charging relay.

 

[YellowT]

Apologies for disappearing from my own thread; unexpected road trip.

I appreciate the responses. I didn't think the "same brand" advice - the question I had originally asked - was correct, but due diligence....

That said, I found a local going-out-of-business sale and snagged another Optima, recently manufactured and same battery type as my original, for half-price. (I won't be replacing my original as it has approx a dozen starts in 30 hours of operation and minimal draw-down housekeeping functions.) Switch and hardware for second battery were already installed, just not the battery. Long story involving a French-made boat, a customer that refused delivery after the dealer began installing accessories, and a resulting cheap purchase for me.

Again, thanks all, for the replies.

 

[airshot]

why would you have a fire or explosion ?, just curious.

from my understanding , correct me if i am wrong , so long as both batteries are 12v , only the amperage could change if both battery's are different to one and other. ? would the alternator only charge and input what the battery's can take.
as i posted , I'm no expert on batteries , but i have jump started may times and never had explosion's , IE one flat battery with not enough amps to kick a motor and the other fully charged , the alternator eventually adds volts to the battery and builds it to a amperage the battery can hold ,no further.

I have jump started hundreds of times with no issues either, but...there are those that have had serious explosions !! I go overboard when connecting batteries to be sure everything is good and proper, never been one to cut corners, but, look around, how many folks take chances,and don't realize them until after a dissaster ? A boat is no place for a fire.....better to be safe !!

 

[pgandw]

why would you have a fire or explosion ?, just curious.

If the batteries in parallel are even slightly mismatched in voltage, you get a lot of current flowing from one battery to the other.

In my case, one of the batteries got a shorted cell, so was over 2V lower than the other when I paralleled them. I had 6 ga parallel cables with no fuses. The parallel cables quickly glowed red hot, and melted the insulation off the wire. The off-gassing from the incoming current caused hydrogen to flow out the vents, which the red-hot parallel cables ignited. Hydrogen makes the prettiest blue flame - ask me how I know.

I put the fire out, which was contained to the battery box (1 box for both batteries), by using lineman pliers to cut one of the parallel cables.

The off-gassing and boiling of the electrolyte blew holes in the tops of both batteries, but no liquid leaks. The bad battery had a lot more holes in the top than the other.

Since this was on my camper, I got rid of the risk by switching to 2 6V GC-2 golf cart batteries. Batteries in series can't do this to each other. If I were 2 have 2 12V batteries again, I would install 50A fuses in the parallel lines. And I would probably not parallel them unless there was a real need to do so. On a boat, use 1 battery for trolling and at anchor, and keep the 2nd for starting the motor to go home. Recharge the 1st battery separately when I got home.

Fred W