SPECIFIC GRAVITY CHECK CHART
The specific gravity of battery electrolyte changes with temperature. Heat thins the solution and lowers the specific gravity. Cold thickens the solution and raises the specific gravity.
A fully charged battery should have a specific gravity between 1.260 and 1.280, with the electrolyte temperature at 80°F. The specific gravity reading must be corrected by adding 4 points (.004) for each 10°F above 80°F or subtracting 4 points for every 10°F below 80°F.
For example: The hydrometer reading is 1.280, and the electrolyte temperature reading is 10°F. According to the chart below, the specific gravity must be lowered by 0.028 points. The true corrected reading is 1.252.
280 - 0.028 = 1.252
You should never take a hydrometer reading immediately after water has been added. The water and electrolyte must be mixed by either charging for a few minutes at a low rate or by allowing the battery to sit for an hour.
A difference of 50 points (0.050) or more between one or more cells indicates a defective battery. It should be replaced.