Need A New Boat Battery

[Ed.]

As I am intending to go offshore in a few weeks time I decided to test my battery, as I had a suspicion that something was not quite right with it, which is just as well I did as it is almost dead.  Funny thing is it charges up OK so I didn't think there was anything wrong with it but did get a low voltage warning on my MFD after starting the motor, most likely a dead cell in it. My existing battery is a 1100CCA size but measured when tested at 55CCA so not good, dodged a bullet by testing it. So today will  be going to order a new battery. Most likely will get the  Century Marine Pro 780 as it is on  a good special at the moment but will also drop in on the way and see about the Cat batteries before I do, as I have heard good things about them. I inquired about those years ago but at the time they were more expensive than the alternatives, they aren't classified as a marine battery but they are much more vibration fortified  than average, which is what a marine battery is, otherwise I will get the Century battery.

[Ed.]

Checked out the CAT 175-4390 battery price  but there were about $48 dearer (even with a 15% discount)  than the Century but only came with a 12 month warranty so I put a  Century Marine Pro 780 on lay-by and will pick it next next fortnight. Got the battery for $211 from BCF on a price match to Batteries Direct,  ended up about $80 less then BCF's normal price. This battery is small compared to the 135A AGM that it is replacing but should do the job as I only have a small 150HP outboard to start.

[benno573]

sounds like a good deal mate.  can never have too many CCA or AH in my opinion!

[GregOug]

2 hours ago, Ed. said:

Checked out the CAT 175-4390 battery price  but there were about $48 dearer (even with a 15% discount)  than the Century but only came with a 12 month warranty so I put a  Century Marine Pro 780 on lay-by and will pick it next next fortnight. Got the battery for $211 from BCF on a price match to Batteries Direct,  ended up about $80 less then BCF's normal price. This battery is small compared to the 135A AGM that it is replacing but should do the job as I only have a small 150HP outboard to start.

Yeah. Only 150hp. That’s a fair sized outboard. Your old battery was 1100cca. Is the new one 780cca or something different? I’d be careful going down in power.

[Ed.]

Hi Greg, when I got that 135AH AGM battery I had a 26ft boat with a 8.1L V8 420HP in it, when I got rid of that boat I put that battery into this one however this battery is supposed to be good for engines up to 350HP with it and  has a 780CCA rating so don't know that 20CCA would make that much of a difference as my motor requires 800CCA, however this battery meets the 1000MCA rating that my motor requires. I spoke to a  Mercruiser mechanic and he said,  no problem.

I tried to find out what size motor you have on your boat but couldn't find it, from memory I seem to recall you have a largish outboard on your boat, if you do, what size is your battery?

[GregOug]

1 hour ago, Ed. said:

Hi Greg, when I got that 135AH AGM battery I had a 26ft boat with a 8.1L V8 420HP in it, when I got rid of that boat I put that battery into this one however this battery is supposed to be good for engines up to 350HP with it and  has a 780CCA rating so don't know that 20CCA would make that much of a difference as my motor requires 800CCA, however this battery meets the 1000MCA rating that my motor requires. I spoke to a  Mercruiser mechanic and he said,  no problem.

I tried to find out what size motor you have on your boat but couldn't find it, from memory I seem to recall you have a largish outboard on your boat, if you do, what size is your battery?

Hi Ed,

Thats a bloody good question! Glad you asked. I have absolutely no idea.

Hold on.

Okay, just went and checked and I have twin batteries, both 900 whatever’s and the engine has 200hp V8 stickers on the side of it.

cheers

Greg

[Ed.]

Are they really big batteries and do you start the motor with both batteries or just the one?

[Ed.]

Just found a pic of your boat, you have the bigger 4 stoke version of the one I have, mine is a 150HP  2 stroke and if your batteries have  900 on the sides it probably relates to the CCA rating so much bigger than the battery I got so can't compare them. As I said the battery states that it is good for up to 350HP so it should be fine (famous last words) . I was thinking about taking my old one as a spare even though it is knacked it still starts the engine fine but don't really want to do that  it as is another 34KG to drag around.

[GregOug]

1 hour ago, Ed. said:

Are they really big batteries and do you start the motor with both batteries or just the one?

No. They are about the size of a normal car battery for a six cylinder. Maybe a little bigger. And I use both to start it.

[GregOug]

53 minutes ago, Ed. said:

Just found a pic of your boat, you have the bigger 4 stoke version of the one I have, mine is a 150HP  2 stroke and if your batteries have  900 on the sides it probably relates to the CCA rating so much bigger than the battery I got so can't compare them. As I said the battery states that it is good for up to 350HP so it should be fine (famous last words) . I was thinking about taking my old one as a spare even though it is knacked it still starts the engine fine but don't really want to do that  it as is another 34KG to drag around.

Maybe look at getting one of those power packs (or whatever they’re called) just in case.

[Ed.]

When you got the boat and motor were you told to use both batteries to start or was it just a personal preference?

 

[Ed.]

I would prefer to get another battery if that was the case (which I probably should do anyway but finances are a bit tight at the moment). Just paid for the boat repair and accommodation for 10 days at Agnes Water, the new battery and various upgrades to the boat for this trip.

[GregOug]

No. But the idea is to use both batteries to start and during the day, then if you are overnighting change to one battery to run the lights etc and have the other to start you next morning.

[GregOug]

If it were me, I’d buy the best battery you can afford, within reason. It’s only a once every few years purchase and could save your life.

[Ed.]

I used to have two big AGM batteries on the last boat and switched batteries overnight, either one could start the motor on its own, and one of them was the current battery that has gone faulty now. The other one went with the boat. As for buying the biggest battery I could afford, I just did as I was told it would be fine, till I got conflicting advice!

[GregOug]

6 minutes ago, Ed. said:

I used to have two big AGM batteries on the last boat and switched batteries overnight, either one could start the motor on its own, and one of them was the current battery that has gone faulty now. The other one went with the boat. As for buying the biggest battery I could afford, I just did as I was told it would be fine, till I got conflicting advice!

Lol. Don’t listen to me! I know nothing!

[Ed.]

Apparently neither do I.

[Drop Bear]

How many years do you reckon you can get out of a battery? 

I really don't wanna be caught out...

[GregOug]

In my experience 3 years or so and you can expect them to go.

[Drop Bear]

14 hours ago, GregOug said:

In my experience 3 years or so and you can expect them to go.

My boat is coming up to 3 years now. I need to do some maintainance, flairs are up, service life jackets and replace batteries by the sound of it. Oh and that pesky 360 white light...

[GregOug]

7 hours ago, Drop Bear said:

My boat is coming up to 3 years now. I need to do some maintainance, flairs are up, service life jackets and replace batteries by the sound of it. Oh and that pesky 360 white light...

Another benefit of having twin batteries is that they’re very unlikely to go at exactly the same time, so you can wait until one does go then replace it, rather than replacing it early because you haven’t got a backup.

[Ed.]

Just got my battery back from Autobarn where I asked them to charge it up for me overnight on their chargers which are  better than the store bought one which I got 15 years ago and is the one I normally use to top  charge it, tested when I got home and the battery voltage is higher than I ever managed before, I will see how much the voltage naturally drops after a day or so, if it stays high I will modify  a battery charger which I made a few years ago and put an extra turn or two on the transformer to give me a higher voltage as both only seem to go to 13.5V so will aim for 14.6 or 15V. The charger I made can put out 20A has a better output which is better than the 8A one I bought from the store. But it is not a smart charger so will have to watch it whilst charging  and maybe charge the battery in two sessions.

So looks like my old battery may still have some life left in it and will use re-purpose  it as the second battery, provided I can keep top charging it up at a higher Voltage and it keeps it's charge. I will pick up some heavy battery cable on Monday and see if I can find some room in the boat for it. It is another 35Kg weight I will be adding to the boat though. Probably will add a pair of 50A Anderson plugs to it in case I want to connect a fridge freezer to it. The boat already has a 2 battery switch in it so hopefully that may make life simpler and safer.

[Ed.]

Just an update, I managed to increase the voltage on my charger, only needed some extra  wire on the secondary side, fortunately there was an little bit of spare secondary wire sticking out the back of the transformer and so I just pushed it through the transformer, rearranged a few things in there because of the now shorter wire stickout and now it is up to 15V unloaded. That saved me from totally unwinding it and putting in a longer piece of wire. Now will just watch what voltage the AGM battery will drop down to over the next few days. Keeping fingers crossed.

[GregOug]

23 minutes ago, Ed. said:

Just an update, I managed to increase the voltage on my charger, only needed some extra  wire on the secondary side, fortunately there was an little bit of spare secondary wire sticking out the back of the transformer and so I just pushed it through the transformer, rearranged a few things in there because of the now shorter wire stickout and now it is up to 15V unloaded. That saved me from totally unwinding it and putting in a longer piece of wire. Now will just watch what voltage the AGM battery will drop down to over the next few days. Keeping fingers crossed.

Sounds like you’ve pretty well got it sussed out.

[Ed.]

Provided the old AGM battery stays at the higher voltage I will be happy, it currently is 12.9V after  10 hours from when I picked it up and I am not sure when they disconnected it from their charger, so I may have lucked in.

[GregOug]

On 14/08/2020 at 8:02 PM, GregOug said:

No. They are about the size of a normal car battery for a six cylinder. Maybe a little bigger. And I use both to start it.

Actually, I looked again. They are a fair bit bigger than the average car battery