Battery Hydrometer Instructions

A battery hydrometer measures the concentration of sulfuric acid and water in each cell of a battery, in a measurement of specific gravity. This is a direct indication of the integrity of the anodes within the cell, and is the only sure method of determining if the battery is capable of holding a charge in every cell. As the anode depletes, the cell's ability to sustain a concentrated concentration of water to sulfuric acid is reduced. Its ability to store energy is seriously compromised. The best time to check the cells is after the battery has had enough time to be fully charged, or during a low amperage episode, as in a hard start. Never check the cells after being watered, as the water will float atop the acid. The primary interest is generated by a cell that has more than a .5 difference in specific gravity. A fully charged, good cell will have a reading of 1.250 to 1.275 specific gravity or higher. Hydrometers have a measurement range from 1.100 to 1.300 specific gravity.

Things You'll Need

• Set of wrenches
• Rubber gloves
• Hydrometer
• Water
• Small common screwdriver

Instructions

1. Disconnect the battery terminals, starting with the negative terminal, using a wrench. Remove the battery caps, using the screwdriver.

2. Check and record the readings from each cell. The hydrometer looks like a big turkey baster, with a ball in the glass tube and specific gravity levels indicated on the side. Insert the hydrometer tube into a cell and draw enough acid into the tube until the ball floats. Look at the side of the tube and read the level of acid adjacent to the numbered mark on the tube. Squeeze the bulb and force the acid back into the cell. Go to the next cell.

3. Diagnose the readings. If any cell showed over a 5 percent difference, the cell and battery is bad. If all the cells were even, but low, the alternator is bad and not charging properly, or the vehicle has a short that is draining the battery.

4. Fill the battery with bottled water, as necessary, and replace the caps. Install the battery terminals.