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Old 21 May 2016, 02:02   #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, 03:26   #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, 08:31   #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, 08:43   #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, 08:47   #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, 10:19   #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, 11:35   #7
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Internal short across two plates possibly in the battery
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Old 22 May 2016, 01:29   #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, 01:46   #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, 02:37   #10
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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.
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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Old 22 May 2016, 04:41   #11
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Originally Posted by Poly View Post
Davie, can we assume with your background that you have eliminated the obvious, like vhf left on, or an auto bilge pump?
Yes, its to do with the auto pump. Design fault but who can work out what was happening?
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Old 22 May 2016, 05:26   #12
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Davie that's why I did away with my auto pump after two burn outs and when back to float switch saves bat power as well as its not pulsing constantly sometimes on a dry well. Hope your sorted now.
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Old 22 May 2016, 06:21   #13
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Yes, its to do with the auto pump. Design fault but who can work out what was happening?
So... if you are happy to go with float switch instead of the auto water sensor you can simply put a float switch in front of the auto supply so that both the float and the water sensor need to go on to pump...?

It only takes water droplets across the electronic sensor to make a circuit and switch the pump on. I get condensation in the bilge of my hard boat sometimes (covered boat - small amount of water in bottom (2 cups full) - heated by cover. 100% humidity I'd guess then cools down, and the humid air touches the cold sides and condenses. That dribbling down the sensor switch will be enough to switch it on.

Remember that the reason these sensors were developed was to stop debris floating into the float switch and either jamming it open (and on) or stopping it opening. If you can address the stopping opening (positioning) the jammed open will still need the electronic sensor to activate as well...
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Old 23 May 2016, 06:51   #14
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The automatic bilge pump skin fitting is directly above the elephants trunk...
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Old 23 May 2016, 07:45   #15
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The automatic bilge pump skin fitting is directly above the elephants trunk...
So the bilge pump outlet is going into the elephants trunk! Genius piece of rigging!
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