one battery or two that is the question

[stepheneyre]

hi all i have just fitted a 150 hp engine to my rib and find the battery struggles to start the engine (had the battery tested its ok and fully charged)

i am thinking do i get a bigger 1 with a higher cranking power or do i put twin batterys on

i have room at the front in the console to do this

if i do twin up do the batterys do i need the same power or can i just connect 2 together + to + and - to -

would 2 affect the electric,s


thanks for looking

any advice would b helpull

steve

[BogMonster]

How big is the battery? Unless it is a bit weedy I don't think it should have a problem spinning over what is only I think around a 2.6L engine.

Anything decent that will provide say 600 amps plus of cranking power shouldn't have a problem at all - that will start a diesel of that displacement never mind a petrol. What CCA and Ah is printed on the battery? If its 70Ah and 600 amps CCA or more then I think you need to look at other causes e.g. faulty connection, bad earth, dodgy starter motor etc.

Unless you have twin engines and separate electrical systems or some sort of split charge arrangement I can't see any real benefit in having two batteries rather than one big one so one big one would be my suggestion. I have heard (on vehicle installations) that two batteries permanently connected + to + and - to - can self discharge due to current cycling between the two when everything is switched off, but I don't know if it is even common or even true - I've not seen it.

Just my 2p, I'm no expert on boat systems but I do spend a fair amount of time peering at vehicle electrics which is much the same as a boat but without the complication of salt water

[codprawn]

My Discovery has a pretty weedy battery - about 75a/hr but it starts a 2.5 diesel even in cold weather = there should be no probs with a big outboard.

IF the battery is fine - and the tests don't always work - then check the cables - either too long or too much resistance etc.

[chewy]

What size cable have you got fitted, welding cable works well!

[dougcrock]

I had probs on previous rib where water had turned copper black and caused loss of power volts to engine every thing looked ok and battery was good had to replace complete starter cables

[PeterM]

I have 2 - one runs the auto bilge pumps & after heavy rain for a few days will struggle to start the motor . So hence having the other one to be sure I have a 'full' battery to start with.

I have also had probs where corrosion of the wiring dropped the voltage to the point of not being able to start the motor - and you only can see/ measure the drop when the battery is underload - again cables replaced & no problems. Cut the sheilding off the cable & you could see the corrosion.

[jambo]

HI Steve, like Blackroady I have two fitted. I use my boat on the wset of scotland and sometimes it maybe 2 weeks in between visits so with rain and natural discharge I have found thru experience that two is best with a battery switch. I have 2 120ah's squadron marines and they work fine. I found last year I was not starting well and my engineer spotted the problem my negative cable from batteries to engine was more than 60% corroded and therefore not enough charge was getting thru to turn my 150 2st mariner. So do achech on your cables especially if there is a long run from consul to engine under deck.
Hope this helps
J

[Downhilldai]

Check the MCA/CCA requirement of your DF150 and, as you have the space, I'd suggest you fit 2 batteries of at least that rating, connected via a changeover switch (batt 1/batt 2/both/off).
Also check the cabling, as mentioned above. The installer of the motor should have done this.

[codprawn]

Originally Posted by Blackroady

I have 2 - one runs the auto bilge pumps & after heavy rain for a few days will struggle to start the motor . So hence having the other one to be sure I have a 'full' battery to start with.

I have also had probs where corrosion of the wiring dropped the voltage to the point of not being able to start the motor - and you only can see/ measure the drop when the battery is underload - again cables replaced & no problems. Cut the sheilding off the cable & you could see the corrosion.

My single 120a/hr battery will start the engine after 2 months of heavy rain and there is no cover on the boat - and Wales is pretty wet!!!

[jambo]

Originally Posted by codprawn

My single 120a/hr battery will start the engine after 2 months of heavy rain and there is no cover on the boat - and Wales is pretty wet!!!

A but prawn you get 'special' rain in wales!!

J