Battery Grade Acid

Specific Gravity

Specific gravity means exact weight. A "Hydrometer" or a "Refractometer" compares the exact weight of electrolyte with that of water. Strong electrolyte in a charged battery is heavier than weak electrolyte in a discharged battery. By weight, the electrolyte in a fully charged battery is about 36% acid and 64% water. The specific gravity of water is 1.000. The acid is 1.835 times heavier than water, so its specific gravity is 1.835. The electrolyte mixture of water and acid has a specific gravity of 1.270, usually stated as "twelve and seventy."

Packagings Of Battery Grade Acid

5 Lts, 10 Lts, 20 Lts, 25 Lts, & 35 Lts

Specific Gravity Readings

By measuring the specific gravity of the electrolyte, you can tell if the battery is fully charged, requires charging, or must be replaced. It can tell you if the battery is sufficiently charged for a capacity (heavy-load) test. The battery must be at least 75% charged to perform a heavy load test. (The heavy load test will be discussed later). In other words, each cell must have a specific gravity of 1.230 or higher to proceed.

If the battery is less than 75% charged, it must be fully recharged before proceeding. If the battery is 75% or higher proceed to a heavy load test. A battery not sufficiently charged will fail because it is discharged.

Specific Gravity - Excessive Cell Variation Readings

Variation in specific gravity among cells cannot vary more than 0.050. The variance is the difference between the lowest cell and the highest cell. A battery must be condemned for excessive cell variation if more that 0.050. In the example below, the highest SG reading is cell #1 (shown in green) while the lowest SG reading is cell #5 (shown in blue); the difference is 0.070 which requires battery replacement. Cell #5 if failing.

Many factors contribute to cell variation; for example, if water was just added to that cell, the cell is then diluted with water resulting is a lower specific gravity reading. Recharging the battery would correct this false reading. In some cases if a battery that has cell variation slightly over the specification and is only about 50% charge, charging the battery at a slow rate of charge (5A) may reduce the cell variation, thus saving the battery.

Specific Gravity Test Procedure (Hydrometer)

  1. Wear suitable eye protection.
  2. Remove vent caps or covers from thve battery cells.
  3. Squeeze the hydrometer bulb and insert the pickup tube into the cell closest to the battery's positive (+) terminal.
  4. Slowly release the bulb to draw in only enough electrolyte to cause the float to rise. Do not remove the tube from the cell.
  5. Read the specific gravity indicated on the float. Be sure the float is drifting free, not in contact with the sides of top of the barrel. Bend down to read the hydrometer at eye level. Disregard the slight curvature of liquid on the float.
  6. Record your readings and repeat the procedure for the remaining cells.

Battery Charging

All battery chargers operate on the same principle: an electric current is applied to the battery to reverse the chemical action in the cells. Never connect or disconnect leads with the charger turned ON. Follow the battery charger manufacturer's instructions. DO NOT attempt to charge a battery with frozen electrolyte. When using a battery charger, always disconnect the battery ground cable first. This will minimize the possibility of damage to the alternator or electronic components in the vehicle. The battery can be considered fully charged when all cells are gassing freely and when there is no change in specific gravity readings for more than one hour.

A slow charge is 5 or 10 amps while a fast charge is generally 15 amps or higher. A slow charge is always preferred.

General rules for charging a battery

Always leave the vent caps in place during charging.

Always follow the battery charger manufacturer's instructions.

Always charge batteries in a well ventilated area, and wear eye protection and protective clothing, such as a rubber apron and rubber gloves.

Always keep sparks or flames away from the battery. (Do not smoke near a battery)

Recharge the battery at the same rate at which it was discharged. If the discharge was slow, then charge at a slow rate; if the discharge was rapid, then charge at a higher rate. (When in doubt always use a slow charge.)

Never charge a battery that is connected to a vehicle. Disconnect the battery and charge. Excessive voltage can damage electrical circuits on the vehicle.

Recheck specific gravity readings periodically, determine if further charging is still required.

Periodically check the battery for excessive heat by placing your hand on the side of the battery. If it is hot (125'F) to the touch, interrupt the charging (turn off) until the battery cools and lower charge rate.

Adding Water

Under the rare occurrence of adding water to a battery, use only Distilled water. Minerals and chemicals that are commonly found in regular drinking water will react with the plate material and shorten battery life. Under normal conditions the addition of water should not be required. However, the addition of water may be necessary when the battery has been overcharged, for overcharging results in excessive evaporation of water from the electrolyte.

The water level should be no higher than 1/8 inch below the bottom of the vent well. To avoid permanent damage, make sure the electrolyte level never drops below the top of the plates. Also, avoid over filling, this may result in electrolyte overflow from the battery.