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If considering only tenths of a volt to precisely determine state of charge.....
When you charge a battery the electrolyte next to the plates becomes acid concentrated causing the battery voltage to briefly falsely read higher than normal....a 'surface charge effect' remaining until either resting time or the motion of the battery causes the remaining electrolyte to remix and only then does the voltage represent the true charge state.
A similar but reverse effect occurs when you load a battery. At 1st the electrolyte next to the plates becomes water concentrated lowering the apparent battery voltage. Resting the battery results in this surface discharge effect being elimintated as the water mixes with the remaining more acidic battery electrolyte...then the battery voltage correctly represents the state of charge of the battery.
Give the battery a while to stabilize both just after applying charge and loading a battery if you want the voltage to represent the true state of charge. If it is in a boat with wave motion, the wait is very short; on the parked trailer it takes much longer....overnite or 24 hours is often cited as a suggested time period.
Last edited by Lou r Pitcher; 05-19-2017 at 12:46 PM.
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New dual-purpose battery seems to have solved the problem. Thanks for the advice and help fellas.
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