TECHNICAL NOTE
TN-09003
Understanding Battery Plate Formation
and Its Effect On Internal Resistance
Scope:
This Technical Note (TN) describes the process of plate formation of a lead-acid battery, and shows a
case history of its affect on a battery’s internal resistance as formation takes place.
Revision: A
Authored by: Rick Tressler & Fran Losey
Approved By: Fran Losey, Director of Technical Services
6 November 2009
Rev. A
Background:
Formation Process
Among the final processes involved in the manufacturing of lead-acid batteries is plate formation. This
process requires considerable time, ranging from hours to days, depending upon the electrical (ampere
hour rating) and formation method used for a particular battery model and technology; VRLA (valve
regulated lead-acid) or VLA (vented lead-acid). For most Manufacturers, once the batteries come off the
formation charge cycle, they are discharge tested once. All passing the test criteria move on the next step
in the manufacturing process. This is generally a full recharge, cleaning and final inspection before
packing and shipping.
Initial Capacity
Formation tends to be a bottleneck in the manufacturing process since all batteries must pass through the
formation area of the plant. Cells are formed to the degree necessary to achieve initial capacity as
specified by the battery manufacturer. Initial capacity is generally found in the performance data sheets
and can be as low as 90% on delivery. Some are rated to deliver 100% of their published performance.
Additional information is documented in the Manufacturer’s data sheet.
Initial Capacity, Internal Resistance and Time on Float
It must be understood that internal resistance at this point is not going to be at its lowest just because a
battery cell is new and has been formed at the factory. Major U.S. manufacturers recommend that a set
of internal, ohmic measurements (in Alber’s case – DC Resistance) be made 6 months to 1 year after
installation and establishment of normal float conditions. Understanding that internal resistance
increases, as a battery sets in an open circuit state, even when new, is evident with loss of capacity.
Resistance will not begin drop until the battery system receives the commissioning charge and a suitable
period of time on float charge has elapsed. The reason for this is the battery is still in the final phase of
formation of the plates while on charge in service. The electrochemical process is well understood by
the battery industry.
Page 1 of 3
TN-09003 Rev A.doc
Content is proprietary, and may not be republished without Alber’s written consent.
TECHNICAL NOTE
Case Point
Based on the points made previously, the internal resistance alarm thresholds of a monitoring system
cannot be a “set and forget” task. Battery data must be reviewed and adjustments made accordingly, as
the Resistance of the cells will drop during this formation phase. This chart is real world data that
clearly illustrates the point.
6115µΩ 9/08 – pre-formation alarm limit set to 7644µΩ at commissioning
4400µΩ 11/08
3700µΩ 11/08
Post-formation alarm limit
adjusted to 4625µΩ
You will note the 9/2008 data point shows a Resistance result of 6115 µΩ. This data was obtained
during the commissioning of the equipment, with the restriction of the charger NOT being able to be
placed online. The higher resistance is due to the battery not having capacity, and is an accurate
measurement of the Battery’s open circuit state.
In November 2008, you see that the Resistance dropped to ~4400µΩ. This was taken after the batteries
were charged and online.
From November 2008 through March 2009, you will see the batteries have gone through a process and
are now stabilized and the plates appear to be properly formed.
Page 2 of 3
TN-09003 Rev A.doc
Content is proprietary, and may not be republished without Alber’s written consent.
TECHNICAL NOTE
What is important to understand is that this is a natural process that requires recognition, and
readjustment of the Resistance Alarm thresholds used by Monitors. When commissioning the
equipment, our recommendations are that a Commissioning Agent set the individual Cell’s Resistance
Alarm limits to 1.25 * the cell’s Internal Resistance. In the illustrated case above, 6115 * 1.25 =
7644µΩ for this particular cell. This was correctly set at time of commissioning.
With the forming of the plates occurring after the commissioning, one can see the result. Following the
completion of the formation phase, I would select the April 15 dataset and readjust the alarm limits. The
cell’s new alarm limit would now be 3700µΩ * 1.25 = 4625µΩ.
There are two points of emphasis that need to be clearly understood here:
1. If the Resistances are not readjusted as outlined here, once the batteries form, the increase
needed to set off a Resistance Test alarm would not be 25% as we recommend, but rather 207%.
a. Alarm limit set 9/2008 = 7644µΩ
b. Cell Resistance following formation = ~3700 µΩ
c. 7644 / 3700 = 2.07…..over twice the Battery’s Resistance!
2. When starting up systems, it is not always possible to have the charger online, due to
construction and startup issues. If a site is commissioned under these circumstances, a follow up
visit should be planned to readjust the Resistance Alarm limits once the batteries are charged. It
is important to note that Alber equipment is accurately measuring the Resistance; the increased
Resistance in the first test is the result of the cell setting at an open circuit state.
A good practice for new installations is to conduct a quarterly or six month follow up service call. The
responsible person would then review such data, find the formation point (if applicable), and then
readjust the battery Resistance Alarm thresholds to 1.25 * the individual cell value.
END OF TECH NOTE
Page 3 of 3
TN-09003 Rev A.doc
Content is proprietary, and may not be republished without Alber’s written consent.