Data Sheet

UB20.241
UB-Series
24V, 20A, DC-UPS
23. APPLICATION NOTES
23.1. BATTERY REPLACEMENT INTERVALS
There are two main causes for battery failures and the need for replacing them:
- Random failures:
Within the defined service life of a battery, random battery failures can happen. E.g. short circuit in one cell, broken
cell connection, acid pollution, mechanical defects, … . Such failures occur randomly and cannot be predicted. The
UB20 has various battery test features included, which periodically test both batteries individually and report such
failures. These battery tests include:
- Battery presence test, performed every 10s
- Battery dynamic impedance test, performed every 4hours
- Charging time period (max. 40h in <10Ah settings and max. 170h in >10Ah settings)
Battery tests start as soon as the batteries are fully charged (the green status LED must be on solid). Battery dynamic
impedance tests need to fail several times in a row before “replace battery” is reported. This can take up to 14
additional hours after the batteries are fully charged.
- Wear-out failures:
The electrical characteristics of batteries degrade slowly over time. Main causes are chemical effects, which can be
calculated. Therefore, battery manufacturers specify the design life of batteries to be able to calculate the expected
service time. The degradation of a battery cannot be easily tested on a running system. Therefore in addition to the
results from the battery tests of the UB20.241 (random failures), a periodical replacement is strictly recommended.
Service and design life of a battery:
Batteries have a limited service life and need to be replaced periodically. The service life depends on the grade of the
battery, which is expressed in the design life. The design life figures can be found in the individual datasheets of the
batteries and is usually specified according to the Eurobat guideline.
The design life is the estimated life, based on laboratory condition, and is quoted at 20°C using the manufacturer’s
recommended float voltage condition. According to the Eurobat guideline, design lives have been structured into the
following different groups:
3 - 5 years: This group of batteries is very popular in standby applications and in small emergency equipment.
This represents a 4 years design life with a production tolerance of ±1 year.
6 - 9 years: This group of batteries is usually used when an improved life is required.
This represents a 7.5 years design life with a production tolerance of ±1.5 years.
10 - 12 years: This group of batteries is used when in applications where longest life and highest safety level are
required. This represents a 11 years design life with a production tolerance of ±1 year.
If the operational parameters differ from those which are specified for the design life, an earlier replacement of the
battery might be necessary. The “real life” is called service life and is defined as the point at which the cell’s actual
capacity has reached 80% of its nominal capacity. At the end of the service life the capacity degrades much faster, so
that a further use of the battery is not recommended.
The degradation of a battery begins with the production date and not with the time when usage starts.
Effects, which shortens the service life of the battery and requires an earlier battery replacement:
- Temperature:
The temperature has the biggest impact in the service life. The higher the temperature, the earlier the wear-out
phase of the battery begins. The wear-out results in a degradation of battery capacity. See
Fig. 23-1 for details.
- Number of discharging cycles:
The number as well as the depth of discharging cycles is limited. A replacement of the battery might be necessary
earlier than the calculated service life if the battery exceeds the numbers and values of Fig. 23-2.
- Overcharging and deep discharging:
Overcharging and deep discharging shortens the service life and should be avoided. Due to the two individual
Feb. 2016 / Rev. 2.1 DS-UB20.241-EN
All parameters are specified at 24V, 20A output current, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
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