Whens the best time to do specific gravity test

[DannyB1954]

Specific gravity of the battery acid will vary by it's temperature. That is why some Hydrometers come with thermometers. If you are using a hydrometer without a thermometer you will get different reading after a heavy charge than when rested, (battery will be warm from charging).

 

[Optimistic Paranoid]

Bit of useless trivia:

In the old days, they used to ship batteries dry and we filled them with battery acid when we sold them.

I have read that for extreme conditions - like Nome Alaska or the middle east, special battery acids with different specific gravities were used to tailor the batteries to the temperature conditions.