Are separate service and starting batteries really necessary?

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Sinbad2222

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I notice that some newly introduced yachts in the Beneteau range, equipped with diesel engines, are fitted with only one battery. Is this cheeseparing at its worse or has recent battery technology now so far advanced that a big service battery can supply very high cranking currents withut coming to harm? If so this seems a significant step forward as all the paraphenalia of relays, split diodes and special switches with their associated rituals can be dispensed with. I would appreciate any advice from battery experts or those using such a single battery.
 
Yes, ideally...

Yes, ideally a boat needs a separate engine starting battery. The one compelling reason is that with the wide variety of power-hungry devices now common on boats, it's only too easy for the domestic batteries to get too discharged to be able to start the engine. So, if there's only the domestic battery (or batteries), there could be a problem.

Remember when boat engines had starting handles?
 
I agree. If a domestic side device develops a problem or a current drain accidently occurrs you're stuffed. You certainly need an isolated starting battery.
 
BAD IDEA...get 2 a starter and dom.

Battery technology still has a long way to go...

If you dont believe us - work out the "Cold" cranking your engine takes..then work out how long you battery will last untill it's below say 80%...you will get 2!
 
Re: How many batteries?

[ QUOTE ]
The wide variety of power-hungry devices now common on boats . . .[unquote]

So what's new about drunk crew falling asleep with all the lights on then?

Seriously, only one battery AND no starting handle is a frightening combination that condemns one to marina-hopping for that shore power umbilical. Yuk!
 
Re: How many batteries?

My Beneteau bought in 1996 only had one 60A battery. I immediately added one more for the services. Five years later after seeking advice from Adverc, I replaced them by 3 105A batteries, two for services and one for the engine.
 
[ QUOTE ]
BAD IDEA...get 2 a starter and dom.

[/ QUOTE ]Bad idea, get six, five leisure/domestic and one engine start - and a starting handle! oops - probably your engine can't be started that way - ah, the joys of "marinised tractor engines".......
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There are two issues here. I have never had a separate starting battery in the sense that one battery was deep cycle and the other a cranking battery. However, I've always had two separate deep cycle banks, one bank at a time connected to domestic duty. I've never had a problem using a deep cycle battery to start my engine, but I would never consider a single battery bank.
 
Re: How many batteries?

One 60A? That's scary! Hopefull that was a First 18!!!

But I doubt you could fit 3 105s in there...

With 2 105s on mine(1 deep cycle (?), the other... the other type) I feel I should have more, and damn glad my engine starts nice and easily.

Jem (hoping I haven't fated myself with that last remark).
 
Not just a bad idea from a safety point of view, but a pain in the arse to put right. The battery box will be built to take just one small battery and all the wires to/from the engine will be a real hassle to change. Or maybe, just maybe, they will have built the boat with a large battery box to take your own choice of battery sizes... nah - got to make sure there's enough room for a "double" aft "cabin" on a 27 footer.
 
What about 2 (or more if necessary) domestic deep cycle for general use with either being used to start the engine and one of those emergency power pack thingies for the day when you manage to flatten both of them?

I don't have one of these but I'm wondering if it might be a good idea. Anyone any views or experiences?
 
Being realistic you don't necessarily need 2 batteries. I reckon a large deep cycle will easily supply start current to a small diesel. A high CCA battery means large crank current foir it's size.
If you can hand start thne you have no problem. If you do not camp on the boat much and can discipline yourself to small discharge with engine not running then no problem. However evntually your one battery will die of old age. Having a second battery will possibly give you a start to get out of trouble by providing another battery in paralell or an altenrative battery.
So it all depends.... olewill
 
Agree with your views re. yacht designers' priorities.

If the setup is like this then the simplest solution would probably be to find a home somewhere else (hopefully close, but not necessarily) for a new domestic battery, including properly secured box and isolator; run a pair of cables back to the existing box, connecting the negatives together and the positive to a VSR fed from the positive of the starter battery. Shift the services positive lead from the starter battery to the domestic side of the VSR, and leave everything else as is.
 
Bad, Bad boy!!! Beneteau!! Two banks!! One for engines, one for domestic.
I also have a solenoid, with activating button on dashboard, which shorts all baattries to engine start in case you flatten your engine batteries due to a problem, I even have two seperate independant batteries to start my genny!
 
One battery .... no problem.

As long as your engine is able to be started by hand .... ie recoil rope starter as in Outboard.

Hand cranking average Diesel ? Are you that Masochistic ?? Bit of S&M never hurt anyone - but no I don't think so.

I don't like the idea of shorting both batterys to one either to start in emergency ... you then have engine dragging good one down and knacked battery calling amps as well .... recipe for 2 dud battery's. No I much prefer start on one or other and only both together when both are healthy.

I think the world of battery's on boats has got to a point of :

a) Well the old way with Battery selector switch worked - leave it alone. (That's me !!)

b) Search out DIY ways of getting round the old battery switch in a) ..... quite a few !!

c) Open wallet and solve it by spending large wads of cash ... and still end up posting questions about flat batterys, additional cahrging etc. as in Wind, Solar etc.

d) Sit back and read all the horror stories, solutions, advice, sales pitch etc. knwoing full well that Maplins and other such cheapo establishments may have some answers ... well that's what I did allied to a) !!!! Flat battery - What's that ??
 
I have Powerbank and it is pretty handy, starts the engine no probs and holds charge very well - better than a standard battery.
As an aside, has anyone ever started a diesel with a hand crank? I've never heard of anyone managing it.
 
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