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Need help. Boat battery diagnosis

The Poacher

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Hi Raiders

I charged my battery yesterday and used my boat today. Ran about 10 kms so i reckon it would have gotten goid charge from tbe 150honda four stroke. Anyway got back near yhe ramp and i turned it off waiting for the ramp to clear and it didnt have enough charge to start. It would turn a little but not enough to kick over. Lucky i was close enough to get in. Would this be the engine not charging the battery. Or, the battery is dead. Its not that old.

Also, who do i call to diagnose and fix.

Until i resolve this i cant fish as i will never know if it will start.

Can someone help?


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Hi Poacher,

Lets start with a few questions.

How many years old is the battery? If the battery is less than 3 years old it should be ok unless it has not been kept in a good state of charge. Batteries do not like being left partially discharged
as the normal process of plate sulphation is not properly reversed if they are not fully charged each time. This can cause the sulphur deposits on the plates to harden and compromise battery life.

Is it a marine battery? If its not then mechanical shock and moderately deep cycling can impact battery life - a car battery used in a boat can have a life of less than 2 years depending on how much ancillary gear such as lights and sounders is running.

Have you ever had charging issues before? Poorly charged batteries means reduced battery life.

Does your boat have a volt meter and if so what is it reading while the engine is running and when its not running. Gauges can be really hard to read if they are not digital but you should expect to see a significant difference between the voltage when the engine is turned off and when its running. Typically a flat battery will be around 12Volts and under charge it will be closer to 14 Volts... most importantly there should be a notable difference when you start the engine.

Running 10ks flat out should put some charge in your battery but if you idled along the alternator output is significantly reduced so that is not a clear indication of anything.

You could take your boat to a dealer and have them check it out but any auto electrician can test the battery using a load tester so I would suggest you remove the battery and take it to an auto electrician to test. He may suggest that you leave it there if its dead flat so he can charge it and then load test it.

If the battery is buggered then it would still be a good idea to check your charging system. If you don't have a voltmeter on the boat then you can buy a battery and charging tester fairly cheaply online.
Personally, I always carry a jump starter although it's only been used for starting other peoples boats!



Edited by fragmeister
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Thanks guys.

Its a marine battery thats relatively new. There is a colouring system that tells you if it needs water and that shows green. Ie ok.

Jim, i drive most distance flat out today Out also idled around adjusting my drift etc. Plus there was a big 8 knot zone. Thanks fir the volt meter tip. I will check tomorow. My guages are all analogue so i dont know how accurate they are. Will charge up tonight and find someone to test them.

Thanks so much for your help so far Raiders. The knowledge you collectibely share is awesome


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my 2cents

Check that the battery connections are tight and clean. Can you move them?

Put a volt meter on the battery and see what numbers you get. Less than 12V is flat

Start the motor and then see what numbers you get. You should see numbers in the 13V range. This means that you are charging.

Consider getting yourself a jump start pack and take it in the boat with you.

good luck!

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Antony has covered it. Do the 2 voltage tests.

With Engine on - if you are getting 13V (and above) your charging system is working. So its most likely:

1. a battery issue (wont hold charge - due to low fluid or cells have collapsed), or

2. the charging current is not getting into the battery (loose or corroded terminals/connections or wiring)

With Engine off - if the battery is reading less then 12V its pointing to a battery issue - even though your indicators are showing green - if it has caps I would pull them off and check the battery fluid levels as a first step. Disconnect the battery and give both the connections and battery terminals a scrub with a wire brush or some sandpaper. Reconnect and coat with grease to slow down further corrosion.

Note: You can get oxide build up between the terminals and connections and it significantly reduces how much charge your motor puts back into the battery and also how much current you can draw to power your start up.

Edited by zmk1962
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Did all the above and sorted it myself (thanks really to fellow raiders). The terminals needed to be sandpapered. The wing nuts needed tightening with multi grips and both batteries were 13volts or more. I also bought an emergency back up for $179- 6 in 1 job with 23 volt or 12 volt output.

Thanks fir the help. Saved me big headaches.


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