Accurate state of battery charge

[Eviltail]

Hello
I have read two contrasting methods of determining the state of charge of a battery. The first requires you to leave the battery for a period of at least 24hrs following charging, without any discharge, and then measure directly accross the terminals with all loads switched off. The second states that the measurement should be made following charging, however it is first necessary to apply a high load to rid the battery of what was called "ghost charge", then the measurement is made as before.
Can anyone advise me as to which method gives the most accurate result? Or are they both synonymous?
Cheers,
John

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[snowleopard]

a battery will show an artificially high voltage for several hours after charging, hence the advice to wait 24 hours. of course that's impractical if you're living on board at the time. if you need an accurate figure, use a hydrometer.

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[Robin]

Snowleopard is right, the hydrometer is best if you have non-sealed batteries. Otherwise an accurate voltmeter, not an on board builder supplied analogue meter but a good quality digital one (fitted or portable) will show a pretty good result if the battery is rested off charge and has been supplying some reasonable current like lights or a fridge for a short time 30 minutes say, not long enough to skew the reading. A 12v battery will read 12.6v - 12.8v if fully charged and rested off charge.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[halcyon]

I have always worked on 12 hours after charge, and 1 hour after discharge.
But all methods will only give you a good guide, as the voltage / capacity varies with air temp, air pressure, type of battery, age of battery, how they are being charged or how they are discharged.

Brian

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[Mudplugger]

John,
for what its worth: http://www.reading-colleg.ac.uk/marine/MarineEO1.html
gives a brilliant guide to 12volt/24volt marine electrics covering the whole subject in a particularly lucid manner, might be worth a look.
Tony.

<hr width=100% size=1>Tony W.

 

[philip_stevens]

tony,
your link does not get me anywhere.


<hr width=100% size=1>regards,
Philip

 

[silverseal]

post for reading college was mispelt.. add an e at the end of colleg

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[philip_stevens]

I noticed the "e" was missing and added it, but I got, and still do, this message -
"The page cannot be found"



<hr width=100% size=1>regards,
Philip

 

[ashley]

correct link

http://www.reading-college.ac.uk/marine/MarineE05.html#TESTING BATTERIES

actually some good info on this site


<hr width=100% size=1>Live life to the fullest... think of all the people on the Titanic who passed up chocolate dessert.

 

[Mudplugger]

SORREE.... Tony.

<hr width=100% size=1>Tony W.

 

[philip_stevens]

No apology needed Tony, and thanks Ashley for the correction.

<hr width=100% size=1>regards,
Philip