1. Battery Research and Testing, Inc.
RESTORING CAPACITY TO A VRLA AGM BATTERY by addition of Water and Catalysts
PES/SCC-29 meeting 9/30/01
Bloomingdale, IL
Peter DeMar
Battery Research and Testing, Inc.

2. Site Conditions Microwave communications site. Twelve cells.
Climate controlled at 65 to 80 degrees F.
Quality communication rectifiers.
On site automatic generator backup.
Infrequent loss of AC power to the site.

3. BATTERY INFORMATION Mfg. GNB Model 75A-23 Rating 825 AH
Mfg Date March 1992
Orientation Vertical

4. Inspection Checks
During each inspection we checked the following items.
Over-all voltage
Individual cell voltage
Individual cell impedance
Cell temperatures
Intercell connection resistance
Ambient temperature
Charge current

5. As found conditions 7/14/00
Average cell impedance 467 microhms. High 592 microhms. Low 386 microhms.
Charge current 3.6 amps.
Ambient temperature 72 degrees.
Average cell voltage of High 2.29 volts. Low 2.26 volts.
Capacity as tested on 5/18/00 was 32% of the published 3 hour rating to 1.75 VPC.

6. Corrective actions Thirty ounces of water was added to each cell.
Cat-Vent assemblies were added to each cell.
All work was performed with the battery in service.

7. 7/14/00 follow up inspection
Two hours after the completion of the Rehydration process we again inspected the battery.
The average impedance had dropped from 467 microhms to 296 microhms.
There were still 3 cells that were substantially higher than the rest. Two of these had been the highest before the process.

8. 7/19/00 load test Battery was reinspected.
Charge current had dropped from 3.6 amps to 2.2 amps in just 5 days.
The average impedance had dropped from 467 microhms to 274 microhms. There were still three cells that were higher than the rest by a significant amount.
We ran the load test at the three hour rate. The battery lasted 133 minutes. Which equates to 66%. This is a 206% increase from the as found capacity.

9. Actions following 7/19/00 load test
An additional 8 ounces of water was added to cells 7 and 8.
The string was placed back on float charge.

10. 6/10/01 load test
The battery was reinspected just prior to the load test.
Float current had dropped to .9 of an amp
Average impedance was 271 microhms
Load test was run at the three hour rate to 1.75 VPC.
Test was terminated at 166 minutes. This equates to 92%. Which was a 288% increase from the as found capacity.

11. Float Voltages

12. FLOAT CHARGE CURRENT
As can be seen there has been a 400% reduction in the charge current required to maintain this battery in a fully charged condition.

13. CELL IMPEDANCE
A= As found on 7/14/00 at an average of 467 microhms and 32% capacity
B = one hour after adding 30 OZ of water to each cell on 7/14/00 average of 296 microhms
C = 7/19/00 average impedance of 274 microhms. Immediately following the load test we added an additional 8 OZ of water to cells 7 & 8.
D = Impedance values just prior to load test on 6/10/01

14. STRING CAPACITY
The capacity on 5/18/00 was 32% and it was restored to 92%, which with more selective watering could possibly reach 95% or higher. We also could have paused the test, jumpered out cell 8 and continued the test, but felt that we had proved our point.

15. Summary
Average impedance dropped from 467 microhms to 271 microhms. These cells were 172% higher that they should have been.
Charge current dropped from 3.6 amps to .9 of an amp. These cells were requiring 400% more charge current than they should have.
String capacity increased from 32% to 92%.

16. Conclusion
The general condition of a VRLA AGM battery string can be determined from a thorough inspection, which includes charge current, and internal ohmic values, as long as the correct ohmic values have been calculated or are known as compared to a load test.
Individual cell float voltages are meaningless in predicting cell capability.
Adding water and Catalysts to VRLA AGM cells will restore capacity that is lost due to either dry out, or lack of compression, and will maintain that restored capacity.