Technical Brief
May 2012
Single-phase battery
Four factors that affect battery life
2. Battery chemistry
Batteries have limited life, usually showing a slow degradation of
capacity until they reach 80 percent of their initial rating, followed
by a comparatively rapid failure. Regardless of how or where a UPS
is deployed, and what size it is, there are four primary factors that
affect battery life: ambient temperature, battery chemistry, cycling
and service.
UPS batteries are electrochemical devices whose ability to store and
deliver power slowly decreases over time. Even if you follow all the
guidelines for proper storage, usage and maintenance, batteries still
require replacement after a certain period of time.
1. Ambient temperature
The rated capacity of a battery is based on an ambient temperature
of 25°C (77°F). It’s important to realize that any variation from this
operating temperature can alter the battery’s performance and
shorten its expected life. To help determine battery life in relation to
temperature, remember that for every 8.3°C (15°F) average annual
temperature above 25°C (77°F), the life of the battery is reduced by
50 percent.
During a utility power failure, a UPS operates on battery power.
Once utility power is restored, or a switch to generator power is
complete, the battery is recharged for future use. This is called
a discharge cycle. At installation, the battery is at 100 percent of
rated capacity. Each discharge and subsequent recharge reduces its
relative capacity by a small percentage. The length of the discharge
cycle determines the reduction in battery capacity.
Lead-acid chemistry, like others used in rechargeable batteries, can
only undergo a maximum number of discharge/recharge cycles
before the chemistry is depleted. Once the chemistry is depleted,
the cells fail and the battery must be replaced.
4. Maintenance
Relative Life
3. Cycling
Battery service and maintenance are critical to UPS reliability. A
gradual decrease in battery life can be monitored and evaluated
through voltage checks, load testing or monitoring. Periodic
preventive maintenance extends battery string life by preventing
loose connections, removing corrosion and identifying bad batteries
before they can affect the rest of the string.
Even though sealed batteries are sometimes referred to as
maintenance-free, they still require scheduled maintenance and
service. Maintenance-free simply refers to the fact that they don’t
require fluid.
140 ºF
60 ºC
Average Annual Temperature
Optimum operating temperature for a VRLA battery is 25°C (77°F).
High ambient temperature allows unnecessary large quantities of
charge current to flow which results in a shorter service life.
Without regular maintenance, your UPS battery may experience
heat-generating resistance at the terminals, improper loading,
reduced protection and premature failure. With proper maintenance,
the end of battery life can be accurately estimated and replacements
scheduled without unexpected downtime or loss of backup power.
Battery life: design life vs. actual life
Determining battery life can be a tricky business. It’s often
promoted based on design life, defined as how long the battery
can be expected to perform under ideal conditions.
Estimating actual battery life relies on taking into consideration
the four factors that can impact affect it.
Single-phase battery technical brief
What can go wrong with batteries?
Battery maintenance for extended life
Plate separation
Repeated cycling (charging and discharging), damage during
handling and shipping, and overcharging
Grid corrosion
Normal aging, operating in an acidic environment and high
Internal short circuit
Heat (plates expand causing shorts), separator failure, handling and shipping, and grid corrosion
External short circuit
Human error (shorting terminals) and leaks
Quantifying the combined effect of the four factors that affect
battery life discussed in the previous page is difficult. You need a
way to determine when a battery is near the end of its useful life
so you can replace it while it still works, before the critical load is
left unprotected. The only sure way to determine battery capacity
is to perform a battery run-down test. The module is taken off line,
connected to a load bank and operated at rated power until the
specified runtime elapses or the unit shuts down due to low battery
voltage. If battery capacity is less than 80 percent of its rated
capacity, the battery should be replaced.
Sulfation of plates
Sitting discharged for an extended period, not on charge or
being undercharged
Excessive gassing
Often due to high temperatures or overcharging
Drying out
Excessive gassing, high temperatures or overcharging
Battery disposal
Batteries that are replaced can still contain a significant amount
of hazardous waste, including the electrolyte and lead. Therefore,
you must comply with EPA guidelines for the disposal of all UPS
batteries. There are essentially two main categories of disposal, one
for spent batteries and another for spills. The primary ways to handle
these two categories are:
Spent batteries
Send to secondary lead smelter for recycling.
Spilled batteries
Place neutralized leaked material into sealed containers and dispose
of as hazardous waste, as applicable. Large water-diluted spills, after
neutralization and testing, should be managed in accordance with
approved local, state and federal requirements. Consult your state
environmental agency and/or the EPA.
One of the most successful recycling efforts in the world is for leadacid batteries. According to Battery Council International, more than
96 percent of lead-acid batteries were recycled between 1997 and
2001. Many states require lead-acid batteries be recycled, and several
options exist to dispose of used batteries, including:
• If you’re engaged with Eaton on a battery upgrade or replacement,
we’ll take your old batteries and recycle them
for you.
• If you participate in Eaton’s UPSgrade program, we take the old
UPS and recycle it. Visit for details.
heck your local phone book for a local recycler, or search for a
recycler at www.earth911/com.
• Some automotive stores accept batteries for recycling.
any municipalities have dump or recycling locations that will
accept batteries for recycling. When disposing of batteries in
this manner, be sure to get a dated receipt clearly detailing what
batteries were dropped off, including quantities with the recycler’s
full name, address and phone noted in the unlikely event you get
Thermal scanning of battery connections during the battery run-down
test identifies loose connections. This test gives you the chance to
see the battery during an extended, high-current discharge. Scanning
should take place during discharge and recharge cycles.
An effective UPS battery maintenance program must include regular
inspections, adjustments and testing, with thorough records kept of
all readings.
Spot replacement of batteries
Batteries in series are similar to a string of holiday lights. When one
unit fails, the entire string no longer works. When a battery or group
of batteries connected in a series ceases to work, not only is the
battery string no longer functional, but it can be difficult to determine
which battery has failed.
The most effective way to combat this potential problem is to “spot”
replace bad batteries that are less than three years old. While the
four factors affecting battery life play a large role in determining when
a battery is vulnerable to failure, there’s no precise way to ensure
that battery failure can be predicted. The only way to identify bad
batteries early enough for spot replacement is through continuous
battery monitoring and scheduled maintenance. Spot replace bad
batteries that are less than three years old and replace the whole
string between the fourth and fifth year.
Lead-acid batteries: good for the environment?
Which commonly used product has the highest rate of recyclability?
Paper? Only 73 percent of paper is recycled for reuse. Aluminum at
54 percent and glass at 25 percent also fall short of the leader. More
than 96 percent of all battery lead is recycled. Lead-acid batteries top
the list of most highly recycled consumer product.
The processes for lead-acid battery recycling support agriculture
needs and enhance energy conservation. Beyond the successful
reuse of nearly 100 percent of the battery components, lead
recycling facilities harness radiant heat from their furnaces to offset
traditional heating costs. Residual sulfur trapped during recycling is
processed into fertilizer. Even the plastic casings are crushed into
pellets and are used to manufacture new battery covers and cases.
Recycling lead is also more energy efficient than smelting or mining
new lead. The recycled lead can be refined into new alloy repeatedly,
giving it unmatched sustainability and cost stability—a trait unlike
most raw materials.
Single-phase battery technical brief
Battery FAQ
Extending battery service life
1. What is the “end of useful life”?
Eaton’s ABM® technology uses a unique three-stage charging
technique that significantly extends battery service life and optimizes
recharge time compared to traditional trickle charging. An integrated
battery management system tests and monitors battery health
and remaining lifetime and provides advance notification to guide
preventive maintenance. Optional temperature-compensated
charging monitors temperature changes and adjusts the charge rate
accordingly to properly charge the battery and greatly extend battery
life. With remote monitoring of the UPS and battery system, Eaton is
able to respond to alarms and real-time battery data to avert potential
battery problems.
The IEEE defines “end of useful life” for a UPS battery as being the
point when it can no longer supply 80 percent of its rated capacity
in ampere-hours. When your battery reaches 80 percent of its rated
capacity, the aging process accelerates and the battery should be
2. What about battery disposal?
It’s imperative that your service technicians adhere to EPA guidelines
for the disposal of all UPS batteries. Remember, it’s the owner’s
responsibility to make sure these guidelines are followed.
3. My UPS has been in storage for over a year. Are the batteries
still good?
Hot-swappable batteries can be changed out while the UPS is
running. User-replaceable batteries are usually found in smaller UPSs
and require no special tools or training to replace. Batteries can be
both hot-swappable and user-replaceable. Please check your user’s
guide for details on your UPS batteries.
5. How is battery runtime affected if I reduce the load on
the UPS?
The battery runtime will increase if the load is reduced. As a general
rule, if you reduce the load by half, you triple the runtime.
6. If I add more batteries to a UPS can I add more load?
Adding more batteries to a UPS can increase the battery runtime to
support the load, but it doesn’t increase the UPS capacity. Be sure
your UPS is adequately sized for your load, then add batteries to fit
your runtime needs.
Battery Backup Time
4. What is the difference between hot-swappable and
user-replaceable batteries?
(in minutes and seconds)
As batteries sit unused, with no charging regimen, their battery life
will decrease. Due to the self-discharge characteristics of lead-acid
batteries, it’s imperative that they’re charged periodically during
storage or permanent loss of capacity will occur. To prolong shelf life
without charging, store batteries at 10°C (50°F) or less.
UPS with ABM
UPS with Trickle Charge
6:00 I
Battery Age
(in months)
Although batteries are sold with a variety of published life
spans, the fact is, some demonstrate a useful life of as little
as three to five years. Eaton’s exclusive ABM technology
significantly increases the life of UPS batteries.
7. What is the average lifespan of UPS batteries?
The standard lifespan for VRLA batteries is three to five years; for
wet-cell batteries it’s up to 20 years. However, expected life can
vary greatly due to environmental conditions, number and depth
of discharge cycles, and adequate maintenance. Having a regular
schedule of battery maintenance and monitoring will ensure you
know when your batteries are reaching their end-of-life.
8. Why are batteries disconnected on small, single-phase UPSs
when they’re shipped?
This is so that they’re in compliance with Department of
Transportation regulations.
Learn more at
Eaton Corporation
Electrical Sector
8609 Six Forks Road
Raleigh, NC 27615 U.S.A.
Toll Free: 1.800.356.5794
© 2012 Eaton Corporation
All Rights Reserved
Printed in USA
May 2012