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When a battery is fresh off charge the terminal voltage can read as high as 14 volts; it will drop quickly to 13.2 V and then slowly to 12.6 V.
This is due to the surface charge. The surface charge must be removed before testing. If the battery has been sitting at least several hours that will do it or the battery must experience a load of 20 amps for 3 plus minutes.
A hydrometer is the best way to test your battery. Get one that reads from 1.1 to 1.28. The ones with little colored balls are worthless.
State of a full charged battery 1.265
Hydrometer readings should not vary more than .05 between cells.
If you have topped up with significant amounts of distilled water the battery should be cycled a couple of times then fully charged before testing.
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