Correct no load voltage of a 12V automotive battery

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Sunny55

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I have a 12v, 40Ah automotive battery. Here's the voltage measured.

No load voltage(2 hours after disconnected from charger) : Near 14V.

I got to know from websites that says a fully charged auto battery should be 12.7V but why is the meter showing near 14v? I only measured it after leaving the battery disconnected from charger for 2 hours. Any idea ?

Thanks
Sunny55.
 



Hi Sunny55,

True battery voltage measurement for lead acid should be done like this :

1. Recharge battery at full level
2. 24h resting
3. New and healthy battery should show 12,72V-12,73V.


Battery needs 24h time of resting for internal chemical process stabilization.


Best regards,
Peter

:wink:
 

It is normal for the battery to have an elevated volt level for several hours after charging.

I have never seen a complete explanation of the cause. I imagine it is partly due to heat generated by current flowing through the battery.

It may also have to do with electro-chemical processes, in the electrolyte, or on the plates.
 

Well, I think is a bit so high this voltage after 2 hours. Have you filled up the battery with water? Too much water can cause problems, as incorrect density (water/acid concentration).

You should also take a look at the voltage of your charger. Maybe it is overchargin the battery. Should give between 13.5V and 14.5V while charging the battery.
 

Voltage should fall slowly and gradually, and this is normal process. If you have rapid decline of voltage battery is bad or a bad process started. You need to wait 24h for measuring real battery voltage and charge state.

Lead acid should be charged with float charge voltage of 13,80V or with cycle charge voltage up to 14,40V. Float is used if battery voltage is over 50-60% of charge state or for standby for long time. Cycle charge voltage is used when battery voltage is under 50-60% of battery capacity. If there is manufacturers datasheet for battery apply manufacturer charging suggestion.


Best regards,
Peter
 

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