Question for the 12v Battery Panel

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KenMcCulloch

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My 85Ah service battery appears to charge to a healthy 12.7V or so. That's measured after charging from the mains, disconnecting the charger and leaving for >12 hrs. The other night at anchor it went from 12.7 down to 12.2 over about 10 hrs when the only loads were the VHF drawing half an amp or so and the GPS probably rather less. No lights lit (independent battery anchor light) and the only other load might have been a couple of minutes of automatic bilge pump whirring. The same battery was able to start the diesel in the morning.

I'm inclined to think the battery is probably reaching the end of its life, a healthy battery should surely not show such a reduction in V overnight (something in the order of 50% discharged) with such trivial loads. Should I plan to replace this battery in the near future, do you think?
 
Was thw 12.2 volt reading with the VHF and GPS switched on ?

The voltage reading no load, and on load are not the same for a given capacity.

Brian
 
Sounds like it is on its way out...try testing each cell with a hydrometer.......I had this problem last season with a new battery.....the dealer tried to convince me that the battery was OK as he tested it with his £500 test meter.......it was not until we tried a very old fashioned load tester across the trminals that we discovered a dud cell!!
 
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Was thw 12.2 volt reading with the VHF and GPS switched on ?
The voltage reading no load, and on load are not the same for a given capacity.


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Brian, cheers for that, I hadn't considered that aspect, the VHF and GPS were certainly both on. Further test to be undertaken in due course!
 
You say it's your service battery, then you say it starts the engine. Which is it? Bad plan to have one battery for both purposes.
 
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You say it's your service battery, then you say it starts the engine. Which is it? Bad plan to have one battery for both purposes.

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Now I wouldn't normally use the word smarterse here, Norman, but I am prepared to make an exception when necessary. I can start my engine with either my starter battery or my domestic/service battery and in this case used the domestic/service battery which I suspected of being a bit low on charge precisely to avoid using the (still fully charged, 12.7V) starter battery until I knew whether the domestic battery would start it or not. OK?
 
Ken, here is a suggestion from Nigel Calder. Test your battery under load. His advice is to check the voltage with no loAd, you said you had about 12.7V, then using a multimeter check for voltage drop whislt cranking your eng for 15 secs. Use your engine cutoff to ensure it doesn't start. If your battery drops it's voltage precipitously before 15 secs are up then there may be trouble. Expect voltage to drop to 10.5 V initially but then decreas slowly.

Worth a try?

Shane
 
Brian, cheers for that, I hadn't considered that aspect, the VHF and GPS were certainly both on. Further test to be undertaken in due course!

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It is most important to let the battery recover under no load whatsoever before reading the voltage in order to estimate capacity remaining.

The voltage on load will vary depending on the load and will be further from the no load voltage depending on the current being drawn.

When doing the test of battery voltage under starting conditions the voltmeter probes must be in contact with the lead battery posts and not anything else including the clamps.
Dirty posts can cause a voltage drop between the post and clamp which sometimes has to be seen to be believed. Some engine and battery combinations can result in a drop to 9 volts.
 
I was trying to help, and don't think that personal abuse is entirely appropriate. Please yerself what you do.
 
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I was trying to help, and don't think that personal abuse is entirely appropriate. Please yerself what you do.

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Norman I find this problem more and more on this forum.......you try and give someone good sound advise and some arse then shoots you down in flames............I am getting to the stage where I will keep my knowledge to myself and [--word removed--] the rest!!! Too many folk on here with their heads up their arses!!!
 
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I was trying to help, and don't think that personal abuse is entirely appropriate. Please yerself what you do.

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I'm sorry if you find the term smarterse abusive. Your earlier post did not however seem to be a response to my question or to be helpful. Cheers.
 
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