Page 29 - Energize Issue 1 2023

TECHNICAL

Understanding design life, service life,

warranty and accelerated life testing

for lead acid batteries

by Chris Searles, BAE Batteries USA, and Michael Schiemann, BAE Batteries, Germany

sers employ stationary batteries best industry practices for maintaining a lead-acid stationary battery to optimize life to 80%
for a variety of applications. of rated capacity. Thus, it is fair to say that the definition for reliability of a stationary lead-
UMost think of stationary batteries acid battery is that it is able to deliver at least 80% of its rated capacity.
serving three major industry segments: To compensate for the loss of up to 20% of its rated capacity due to ageing and thus
telecommunications, data centres/UPS, provide 100% performance as required by the duty cycle at end of life, IEEE 485 practice
utilities and industrial. But within each recommends adding an ageing margin, sometimes referred to as an ageing factor, of
of these groups are several subsets of 125% when sizing a battery for a given load and duty cycle. Therefore, when IEEE 485 is
application parameters that introduce used in sizing a battery, it is customary to expect that the battery will handle the defined
unique impacts upon the stationary and required load or duty cycle for its full stated life. For a 20-year battery, we are often
battery installation and expected life. surprised that if we run a capacity test at year 17, or even year 15 or 12, the capacity
Battery manufacturers design a measures less than 80%.
battery to do certain things within a Our first thought is to think that we have a bad battery, and we should blame the
given set of parameters. This design manufacturer for a “defective” battery. We are often befuddled when the manufacturer
life is generally predicated on certain pushes back and states that the situation is not covered under warranty. Now this is not to
conditions that may be generic to the say that a battery may not have achieved its full life potential when it should have. However,
specific application. Separate from this, the answer as to why the battery did not achieve its fully stated life is a bit more complex
but integrated in some fashion, is the than just saying the battery is bad or defective.
warranty against manufacturing defect
that forms the manufacturer’s warranty To understand this, we need to answer several questions:
statement. • What was the manufacturer’s stated design life for the battery?
On the other hand, additional factors • Does the manufacturer distinguish design life from warranty?
have a profound effect on the actual • What is the expected service life based upon actual installation and service conditions,
service life of the batteries once installed. and how does it relate to design life, and affect warranty?
These circumstances can also have a
profound effect on how long the batteries Let’s see if we can put all of this into perspective and provide some insight into the reality
will perform at >80% of capacity. of design life vs. service life and put both in the context of warranty. Also, what role does
In the meantime, certain standards, accelerated life testing play in this?
including IEEE 535, mandate battery
evaluation procedures that will provide What is Design Life?
a predictable expected life from the We often hear that a stationary battery is designed for a telecommunication application,
batteries. In Europe, certain testing or it is called a UPS battery, or the literature states that a model is defined as a general-
mechanisms are required to certify a purpose battery. What do these terms mean? Is it fair to say that any battery can perform
battery meets published criteria and the any application, or is it more accurate to state that certain types of batteries will perform
laboratory testing contributes values that better or longer in certain types of applications? Or are both statements actually true.
lead to expected life under normal service The answer to the questions above lies in answering two important questions that
conditions. only the user can answer: How long should the battery last in the application for which
Add to the equation the fact that I am planning to use it? And, how well will it handle the specific application for which I
European manufacturers may offer am specifying the battery, i.e. what are its performance characteristics for this type of
a different warranty for the same application?
battery in the US, and the user can be The IEEE Stationary Battery Committee is in the process of revising two best practices
understandably confused. that will provide guidance in these areas when released – IEEE 1189 and IEEE 946. IEEE
It is accepted industry practice that a 1189 is being rewritten as a guide for the selection of stationary batteries for the majority
battery is considered “good” or reliable of stationary battery applications, in addition to Valve Regulated Lead Acid (VRLA) batteries.
as long as it can deliver ≥80% of its rated IEEE 946 is being rewritten as IEEE Recommended Practice for the Design of DC Auxiliary
capacity. IEEE 450 and 1188 prescribe Power Systems.
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energize | Issue 1 2023 | 29