ET online
November 2007
Q and A - battery testing

Q and A - battery testing

02 November 2007

The following is a series of frequently asked questions from users like you covering various aspects of battery testing:

Q: Why shouldn’t the specific gravity of a Ni-Cd battery be under 1.15?

A: The minimum specific gravity value of a battery should be defined by the appropriate battery manufacturer. The specific gravity is a measure of active material dissolved in water that forms the electrolyte. As the level of active ingredients fall, the specific gravity drops. This reduces the chemical reaction available in each cell which will reduce the output of the battery.

Q: Why is it indicated that the BITE 3 is used to test Lead-Acid batteries and the BITE 2 is used to test both Lead-Acid and Ni-Cd Batteries?

A: The BITE 3 uses a dual tip probe that both supplies current and measures impedance. The problem arises from the stainless steel hardware used with Ni-Cd batteries. The resistive properties of stainless steel cause problems for dual-probe devices. The BITE 2 and 2P does not use dual tip probes. Instead, it supplies 10 A to the entire string instead of a lower value to each individual cell. Therefore, you can use a BITE2/2P for testing Ni-Cd batteries, not a BITE3.

Q: If you were take the same measurements with both a BITE2 and BITE3, would you get the same results?

A: Not necessarily. When performing ohmic measurements the same make and model instrument should be used to ensure consistent results.

Q: Which is a better method of measurement…resistance or impedance?

A: A battery has resistive and capacitive, as well as inductive elements within it. Performing a resistive measurement only determines the resistive properties of the battery. It ignores the capacitive and inductive properties of the battery. Performing an impedance test measures all of the different properties of the battery. For example, resistance is not affected by negative plate polarisation or lug rot, where impedance will be.

Q: Is there an economic justification for performing impedance type battery tests?

A: Yes there is. To perform a discharge test, a battery bank or battery must be taken off-line. A lengthy discharge test is then conducted which also further shortens the life cycle of the battery. The usual interval for such a dis charge test can be extended by augment ing the process with regular impedance battery tests. It extends battery life, saves time AND impedance testing can be performed without taking the batteries off-line.

Q: What is the proper procedure for testing a new battery string installation?

A: During installation of a new battery string, a low resistance ohmmeter (DLRO) can be used on the offline string to verify the strap resistance. Impedance testing should not be per formed on a new string until all installation has been completed. For VRLA we recommend a minimum of 30 days of service prior to performing an ohmic test. For flooded batteries, they should first be fully charged and tested within 60 days of installation. After the installation is complete the BITE can be used for such a test. Please be sure the probes are on the strap and not on the hardware.