A conductance baseline reference value is a benchmark value based on data collected from known good batteries. Reference values provide an estimate of where a reading should be, although they are not absolute. The trending of actual measurements is the best method of interpreting conductance measurements.
Determining Site Specific Baseline Values
The best baseline is one established for that specific battery installed at the site within 90-180 days of the installation.
- Ideally, the individual conductance value should be measured at installation and again after the battery has been on float charge for at least 72 hours in order for it to reach a high state of stabilization.
- These initial "site-specific" values should be recorded and permanently affixed to the battery as a baseline for subsequent tests over the life of the battery.
- The conductance value will typically increase between the initial installation and after being on float charge for 90-180 days (5% to 15% depending on battery type and size).
- When taking the next conductance test 90-180 days after installation, compare the present test result to the initial installation conductance test result.
- Use whichever value is greater as your baseline for that particular battery at that site going forward.
Note: A battery tested "ON-LINE" may display a different value than when tested "OFF-LINE" due to the charger circuit and load across the battery. Always test the same way, either on-line or off-line, to have consistent and meaningful results.
Testing a Sample of New Batteries
A sample of new healthy batteries can be tested to obtain a baseline value representative of a new battery.
It is best to have a sample size of at least 30 batteries from one manufacturer with the same make, model, amp-hour rating, age (within 6 months), and manufacturing lot.
Record the following information about the batteries:
- Battery manufacturer
- Model number
- Date of manufacture
- Manufacturing lot number (if available)
- Battery temperature
- Has the battery had a freshening charge or not
- Battery voltage
- Conductance test value
Calculate the average conductance value of the batteries. Do not include batteries that are higher or lower than 30% from the average because they might be outside of an acceptable range.
Use the average value as a baseline starting point for this model battery.
Note: For maximum accuracy and consistency, batteries should be tested when in a fully charged state.
Using a Generic Baseline Value to Get Started
When testing new batteries, a generic reference value can be established or employed.
A generic baseline value for a specific battery model can often be found on the Midtronics Stationary Power website or from the battery manufacturer. While it is important to note that the use of generic reference values are not as "accurate," it is still possible to identify grossly failed batteries and significant changes in battery condition by applying this method. The best practice is to establish individual battery baselines as described above and trend accordingly using good record keeping.
When testing older batteries for which no initial site-specific conductance value is available, reference values can be obtained in the following ways:
- Use conductance readings of recently installed batteries of the same manufacturer and model of the battery
- Contact Midtronics or the battery manufacturer for assistance
- Consult your company documentation to see if reference values were created for the battery you are testing.
Note: Generic baseline values should only be used as a guide when no other data is available. Generic values are typical averages to be used as general guidelines only; the best practice is to establish your own relevant baseline values using the method described above.