Monitoring
A battery monitoring system reads every block in a UPS battery string, all the time: its voltage, its internal resistance and its temperature, along with the string's current. It raises an alarm when a block drifts, records every discharge, and shows which block to replace before it takes the string down with it.
It measures every block's voltage, internal resistance and temperature, and the string's voltage and current. Vertiv's data sheet for its Albér BDS-256XL describes a system that continuously diagnoses cell voltage, overall string voltage, current and temperature, and runs automatic periodic internal resistance tests to verify the battery's integrity. Its BDSU-50 guide adds string float and ripple current, ambient temperature and the resistance of the inter-tier connections.
Two of those readings are the heart of it. Resistance rises as a block ages or fails, so its trend shows a weak block before a discharge does. Temperature drives ageing: ASHRAE's power equipment paper gives 25 °C as the ideal for lead-acid batteries and a rule of thumb that their life halves for every 8 to 10 °C above it.
Periodic testing takes a snapshot at each visit; a monitor takes one every few seconds and a resistance reading on a schedule. EnerSys recommends internal ohmic measurements at quarterly intervals, following IEEE-1188, and C&D gives the rule for reading the trend: a change of less than 20% over time is acceptable, more than 50% needs further attention such as a load test. With quarterly readings, a block can fail between visits. A monitor such as the BDS-256XL scans voltages, current and temperature every four seconds and compares them with alarm levels set by the user.
Vertiv's reliability study found an increased mean time between failures for sites with a battery monitoring appliance compared with regular battery service alone. Periodic service does not go away: the battery testing and replacement service still runs capacity tests and inspects what no sensor sees, such as bulging jars and corrosion.
Because ohmic readings on a string that is online can be disturbed by the UPS itself. Vertiv's BDSi data sheet states that other monitors' internal ohmic readings become inconsistent as the UPS load varies, because of variations in AC ripple on the battery, and that its DC resistance test is not influenced by ripple. Whatever the make, the question to ask is the same: are the readings repeatable on your UPS at your load, so that a change in the trend means a change in the battery? A trend built on noisy readings produces false alarms, and false alarms get ignored.
An alarm for any reading outside the limits set for it, at two levels. Vertiv's BDSU-50 guide states that every monitored parameter can have its own alarm threshold, high and low, set per block or globally, and that alarms can latch and drive either a maintenance or a critical alarm contact. Its BDSi has one contact for critical alarms and one for maintenance alarms; its BDS-256XL adds programmable contacts and automatic dial-out notification.
Those alarms leave the battery room through contacts, Modbus or SNMP, into a BMS, a DCIM platform or a monitoring service; remote UPS monitoring covers routing and response.
Every block's voltage, the string current and the temperatures, from start to finish. The BDSU-50 guide describes a discharge mode that detects the event and logs battery voltages, temperatures and discharge currents into an embedded database, for playback in real or accelerated time. A real utility outage then becomes a free capacity check: it shows which blocks fell first and how much runtime the string really delivered.
During a planned capacity test, real-time viewing lets the operator stop the discharge before a block reaches a hazardous point, and the BDS-256XL can control a load unit to run the capacity test itself. How capacity and runtime relate to age and temperature is covered in the UPS battery life guide.
When the string is large, the load is critical, or nobody visits often. A monitor pays off where one weak block can drop a long string, where a site is unstaffed, or where quarterly readings are hard to schedule. Some UPS battery cabinets are built for it: Vertiv's BDSi installs in the UPS battery cabinet, with one controller for up to six cabinets.
For a small single-phase UPS with one short string, periodic testing and timely replacement usually make more sense than a permanent monitor. Whichever you choose, the replacement blocks must match the string; data centre UPS replacement batteries are listed on the battery page for data centre UPS, and battery repair and replacement by UPS brand covers the service side.
Every block's voltage, internal resistance and temperature, plus string voltage and current; many also read ripple current and the connections between tiers.
No. It replaces the quarterly ohmic snapshot with a continuous trend, but capacity tests and visual inspection still need a visit.
C&D treats a change under 20% over time as acceptable and more than 50% as needing further attention, such as a load test. Compare each block with its own baseline.
Some can act on it: Vertiv's BDSU-50 has a charger control relay that shuts down the charger when thermal runaway is detected.
Usually, through Modbus or BACnet, or SNMP for network management. Critical alarms should also reach the people who respond.
Sources, checked 2026-10-04:
Tell us the site, the UPS and the timing. We reply and quote within 4 business hours, or call 1 (438) 800-0382
Brand names are trademarks of their owners and are used only to identify the equipment we service. We are not the manufacturer and are not affiliated with it.