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Old 21 May 2016, 03:02   #1
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Flat battery

Every now and again the battery is totally flat on my rib when left in the water overnight. Battery will be ok for 1 day, 3,4,5 days whatever. You couldn't make this up. Why?
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Old 21 May 2016, 04:26   #2
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Davie, can we assume with your background that you have eliminated the obvious, like vhf left on, or an auto bilge pump?
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Old 21 May 2016, 09:31   #3
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I've seen this before. You may have a loose electrical connection, start with the battery connections (they can be touching the posts but won't flow power). Trace and jiggle up to the engine/console. Wiggle each section/piece/part. Really helps if you have a multimeter.

Everytime Ive seen this it was the battery cable and/or connectors to the batters or lugs.


Good luck
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Old 21 May 2016, 09:43   #4
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Battery isolator work okay? Take a multimeter and test voltage. A healthy battery should give you at least 12.4 - 12.6v.

Is the battery serviceable? I check periodically if the electrolyte solution is covering the cells. If not - top up slightly with distilled water.

Any wiring under the deck that could be chaffed and subject to water through the internal trunking is another possibility which is grounding itself.
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Old 21 May 2016, 09:47   #5
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If it has been flattened a few times and left like that it will never be as good again.
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Old 21 May 2016, 11:19   #6
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With everything switched off, you could try disconnecting one of the battery terminals and connecting your multi-meter in-line. Set it to amps and see if there is any reading, if so the fault is with wiring or equipment. If not it looks like the battery has seen better voyages.
Good luck!
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Old 21 May 2016, 12:35   #7
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Internal short across two plates possibly in the battery
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Old 22 May 2016, 02:29   #8
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I/we have a similar problem with our sailing club rib, so some very useful things to try here thanks for the posts!
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Old 22 May 2016, 02:46   #9
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If it holds charge and you don't have an issue when left on land it's unlikely to be the wording unless you have wires that are shorting out with e boat movement.

I'd be checking the battery isn't shorting a cross the plates with the movement or getting cold! Batteries on their way out fail when cold, if left on the water it could be colder than normal so a cell goes down.
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Old 22 May 2016, 03:37   #10
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Quote:
Originally Posted by treerat View Post
If it holds charge and you don't have an issue when left on land it's unlikely to be the wording unless you have wires that are shorting out with e boat movement.
Or being wet? i.e. a current path created from say a deck fitting through water to the engine leg and back to battery earth. High water resistance so low current so fuse doesn't blow but over several days the current drains the batty...

As suggested you need to see if amps are moving out the batty or not. If not its the batty, is so you need to stop them moving!
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