How to check the specific gravity of a battery?

• There is one way to know the state of charge of battery is to know the amount of sulphuric acid left in electrolyte. This can be found out with the help of a battery hydrometer.
• If the battery is fully charged about 39% acid and 61% water present in the electrolyte. When the battery Is discharged it is about 85% water and 15% acid.
• The battery hydrometer cannot measure the percentages but it measure the specific gravity of electrolytes. It is made up of a glass tube containing a weighted float with markings on its stem in so that the specific gravity readings can be taken directly.
• At one end of the glass tube is fitted a rubber bulb and on the other a flexible suction tube. When the electrolyte is drawn inside the tube, the float rises or sinks, depending upon the gravity of the electrolyte.
• The specific gravity reading can be taken form marks on the float stem.
• Read of specific gravity and state of charge of battery 

          Reading                                               Condition                                                                  

               1.260-1.280                                         Fully charged  

                 1.230-1.260                                         75% or 3/4 charged

             1.200-1.230                                         50% or half charged

           1.170-1.200                                          1/4 charged

           1.140-1.170                                          Very little charged 

           1.110-1.140                                          Discharge