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.

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.

BATTERY INFORMATION

• Mfg. GNB

• Model 75A-23

• Rating 825 AH

• Mfg Date March 1992

• Orientation Vertical

Inspection Checks

• During each inspection we checked the following items.

1. Over-all voltage2. Individual cell voltage3. Individual cell impedance4. Cell temperatures5. Intercell connection resistance6. Ambient temperature 7. Charge current

As found conditions7/14/00

• Average cell impedance 467 microhms. High 592 microhms. Low 386 microhms.

• Charge current 3.6 amps.

• Ambient temperature 72 degrees.

• Average cell voltage of 2.266. 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.

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.

7/14/00 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.

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.

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.

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.

Float Voltages

2.22.212.222.23

2.242.252.262.27

2.282.292.3

7/14/00b 7/14/00a 7/19/00 6/10/01

High

Average

Low

FLOAT CHARGE CURRENT

3.6

2.2

0.9

0

0.5

1

1.5

2

2.5

3

3.5

4

7/14/00

7/19/00

6/10/01

CELL IMPEDANCE

592

467

386358

296253

337

274239

314271243

0

100

200

300

400

500

600

7/14/00b 7/14/00a 7/19/00 6/10/01

HighAverageLow

STRING CAPACITY

32

66

92

0

10

20

30

40

50

60

70

80

90

100

5/18/00

7/19/00

6/10/01

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%.

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.