What new battery?

[pedroofn19]

I have a 1991 90hp 2 stroke Mariner outboard I need to get a new battery for it. After looking on the internet at batteries Im a little confused. Deep cycle or starting battery? The only electrical devices on the boat are a fish finder and bilge pump. Am I right in thinking the bigger the better as in 110ah and 1000cold cranking ampes? Or will that be too much for the engines electrics?
Thank you for reading.

 

[Sandbank]

Re: What new battery?

From my knowledge, if you only have a single battery (appears you do) a starting battery would be better. Deep cycle batteries are designed to be discharged then recharged in order to keep their life. Constanty taking a bit of charge from a deep cycle shortens its life. Make sure you get a gell battery(or at least not an open cell lead acid battery-due potential spillage and acid danger). Bigger may be better to a point as you have to way up weight and size, which could effect your trim. Then again too big just wastes moneyand weight.
Bilge pump usage in amps is probably negligable (unless your boat constantly floods!). Check the amperage usage of the fish finder and how many hours on average you would use it with motor off in one go. This will give you the power required without alternator recharge. I dont think starting batteries are designed to fall below 80% (9.6V), so with this in mind work your equation backwards to find out how many Ah you need in your battery ontop of the starting cranking power required. The manufacturer or your battery guy should be able to assist with the cranking Ah required of the engine but I would have though an 85Ah would do it.

 

[pedroofn19]

Re: What new battery?

Yes I only have the one battery, my engine is a reallly hard to start sometimes and it can drain the battery of power most times. Will a starting battery run out of power faster than a deep cycle battery?

 

[Sandbank]

Re: What new battery?

Starting batteries are designed to give short bursts of high Amps, rather than sustained usage at lower amps. Should u decide to go for deep cycle instead a few formulas that may assist:
At fixed voltage Amps drawn=watts required/voltage
Amps x hours used =Ah used
As a deep cycle should not be taken below 50% discharge (so add 10% to be on the safe side)
Ah required= Ah used/.6

 

[pedroofn19]

Re: What new battery?

Ok sandbank thanks for such a detailed reply, Im very greatful.
But I dont really understand what you mean, Im not very clued up on electricals. I understand that starting batteries are good for the high amperage for a short burst, but will it loose power quicker than a deep cycle battery?
Thats why I thought the bigger the better and deep cycle was the way to go.
Sorry for being so ignorant but I really dont have a clue as you have probably worked out by now.
Thank you very much.

 

[Sandbank]

Re: What new battery?

Sorry to confuse you mate. I have used the following examples that may held. Note there is no proper formula to convert CCA (cold cranking Amps) to Ah.
ifyou reference CCA, Mercury reccomend for a 115 hp a CCA of 500 to 650 CCA with a medium electronics load on a starter battery-good start if you reference CCA.

Looking at the Ah:take a lowrance HDS7 for eg, uses .8A so if you use for 6 hours would be 4.8A. If you started with an 85Ah would be down to 94% and then if you took 12 starts at 30 seconds each (having a bad day!) battery would be down to about 84% which is in the danger zone. Increasing to 95Ah minimum would give you room to move.

Hope it is as clear as mud now! Batteries are an art and a science!

 

[pedroofn19]

Re: What new battery?

Ok thanks sandbank that is a bit clearer now. My engine does have a bad day quite often but I guess that could be down to having a bad battery. I never knew that there were so many types of battery. I now know that my battery is usless and that is why my engine has been so hard to get going.
"Batteries are an art and a science" you are right there mate. Thank you for your input it helps a lot.

 

[fucawi]

Re: What new battery?

there are not many types of battery ...only batteries with different labels and differen prices ...so called starting and leisure batteries are both the same and the only other one is a deep cylcle type with thick plates used in fork lifts etc .

Just buy the biggest lump of lead you can get for your money and keep the warantee ...K mart with a sale day is good

 

[pedroofn19]

Re: What new battery?

Yeah thats what I was thinking, the bigger the better. Thanks fucawi.

 

[fucawi]

Re: What new battery?

I see you are in the uk ..you will find the best deals on e bay inc free delivery ..friend just bought a bosch battery for his Mondeo for 35.99 quid inc post thats cheap

 

[Sandbank]

Re: What new battery?

further to Fucawi's comments, I suggest you go for an automotive gel type as if u go for a Marine battery, the M word will double the price! Supposedly Marine batteries are more rugged but in my experience unless ur a pro and slamming the boat day in and out, automotive do the job fine.

 

[M9.9]

Re: What new battery?

Hi all, You might go with a deep cycle w/the largest amp rating. If your engine has continual 'bad days' you may consider having it tuned-up as too many bad days can and will shorten the life of the starter and the battery. Know doubt if it's a ninety, it will have a charging circuit that will top-up the battery moments after starting on good days.

 

[Ike-110722]

Re: What new battery?

Pedroofn, I suggest you study up on batteries. Unfortunately there is a lot of misinformation rattling around the internet about batteries and it can be very confusing, but there are some good sources that break it down to basics. Start with:
Batteries: Everything You Need To Know http://newboatbuilders.com/docs/BatteriesEverything.pdf
Batteries: Group Number. Does Size really Matter? http://newboatbuilders.com/docs/Battery_Size.pdf
Basic Electricity: Batteries. http://newboatbuilders.com/pages/electricity3.html

and what is probably the mother of all Battery links
Car and Deep Cycle Battery FAQ. http://www.batteryfaq.org/

 

[dwparker99]

Re: What new battery?

Pedroofn, I suggest you study up on batteries. Unfortunately there is a lot of misinformation rattling around the internet about batteries and it can be very confusing, but there are some good sources that break it down to basics. Start with:
Batteries: Everything You Need To Know http://newboatbuilders.com/docs/BatteriesEverything.pdf
Batteries: Group Number. Does Size really Matter? http://newboatbuilders.com/docs/Battery_Size.pdf
Basic Electricity: Batteries. http://newboatbuilders.com/pages/electricity3.html

and what is probably the mother of all Battery links
Car and Deep Cycle Battery FAQ. http://www.batteryfaq.org/

X2. Great advice.

 

[fucawi]

Re: What new battery?

There is also a lot of bull**** centred around getting more money out of you.....there are auto starting batteries and everything else other than a fork lift traction battery is a starting battery with a fancy label ...."Marine" "Leisure " " Dual Purpose"

The extra paid for a 2 3 4 year warantee just ensures the maker is still in profit if he has to replace it ...same battery ..

CCA for a auto battery is at -18 deg C for a marine battery so called at 0 deg C ...makes it look better . To convert marine to auto multiply by 0.77

Now you all go buy the biggest lump of lead you can get for you money and keep the receipt ...

 

[pedroofn19]

Re: What new battery?

Ok guys I think I know what I need now. i thank you all very much.