Page 30 - Energize Issue 1 2023

TECHNICAL

However, in order to understand the in DIN standards, e.g., DIN 40742 (gelled electrolyte single 2 V cells) or DIN 40744 (gelled
expected life of a given battery type we electrolyte multi-cell block units). Today these standards, still referenced in literature, have
really need to begin with its design life. been incorporated into the global IEC body of standards, such as IEC 60896-21 or IEC 60896-
The design life should not be compared 22. In Europe, there is a distinct way that batteries are considered. Table 1 defines these
with service life as the two are actually distinctions.
separate. And neither should be confused
with warranty. It was common to state that batteries would endure for a period of years depending
First, like so much of what we upon type, regardless of manufacturer, in order to facilitate common expected results. In
4
experience today, there has been an Germany, these endurance characteristics were divided into three subtopics :
evolution in both the manufacture and • Endurance in float service
the use of stationary batteries. In its early • Endurance in overcharge
history, the stationary battery was a pure • Endurance in cycles
lead cell encased in a rubber container
and the plates were separated by rubber In an earlier Battcon paper it was stated that some preliminary testing results suggested
or wood. Its application was fairly simple that a 20-year design life for a VRLA was possible. 5
2
as well. Europe took a different tack. The Eurobat Guide for the Specification of Valve Regulated
Today we use stationary batteries Lead-Acid Stationary Cells and Batteries defines design life as follows: “The design life is
to back up cellphone sites on mountain the estimated life determined under laboratory conditions and is quoted at 20°C using the
tops; switchgear in utility and industrial manufacturer’s recommended float voltage conditions”. 6
control houses, and central offices spread To facilitate user requirements, design life was sometimes called expected life which
throughout the landscape; UPS in cloud was structured into four main groups as shown in Table 2.
data centres; motors, pumps and turbines
in power generation plants including Note 1: “The following characteristics may be qualified by test methods in the International
nuclear Class 1E sites; and to store electric Specification, IEC 60896-21.”
energy and provide backup power for use Note 2: “This description applies equally to ‘Absorbed (AGM)’ and ‘Gelled’ electrolyte.”
in photovoltaic or wind installations. Note 3: It was recognized that this was not to be considered a standard, and that
As a result, battery manufacturers “the classifications were arbitrary with overlaps so that the four groups could not be
make Planté plate, flat plate and tubular distinguished clearly. 7
plate cells, some with thin or thicker
plate construction, some with pure lead, How does design life differ from service life?
others with lead antimony, lead calcium This takes us to the tricky part: “How come I bought a battery with 20-year design life, but
or lead selenium alloys; both VLA cells I only get 15 years or less from my battery?” We must discuss service life and understand
and VRLA cells – many with an absorbed how it differs from design life.
glass mat (AGM) topology and others with First, let’s define service life. Service life has been defined as the “period of time during
a silica that produces a gelled electrolyte which, with a given load and by following the maintenance instructions, the specified limits
concentration(GEL); and now with the
advent of newer technologies (many yet
to be proven for cost-effective applicability
for stationary application) we see lithium,
sodium or flow type battery models, to
name only a few.
Each of these were designed to meet
certain criteria, taking into consideration
the alloys, grid structure, electrolyte,
topology and expected usage. This resulted
in a 20-year, 10-year, or possibly other
stated design life.
In Europe, design life is applied to Table 1
components used in the battery and the
limiting factors that might affect lifetime as
established from endurance. Endurance
3
values are the result of combining
standardized and accelerated testing
results. For example, in Germany, battery
manufacturers designed and tested lead-
acid batteries to certain criteria defined Table 2

energize | Issue 1 2023 | 30