UPS systems are an effective and established way of protecting yourself or your organisation against unexpected power failure. They are able to respond immediately and can prevent systems from going offline. Whilst they can provide cover before the main backup power kicks-in (or the mains power is restored), it is important to note that they are not in themselves a complete backup solution. Timing your UPS battery replacement is also extremely important.
Types of UPS battery
There are three main types of UPS batteries available: Lithium-ion, lead-acid, and sealed. Each has its own pros and cons. Because they are so important, it is crucial that UPS batteries are regularly tested. There are several different types of UPS battery testing that are commonplace.
Impedance Testing
Impedance testing for UPS batteries is a non-intrusive method that is designed to identify early signs of battery weakness or deterioration of individual cells within a battery. As it is non-invasive, it can be carried out on a live working battery system ‘in situ’ and usually takes only a few hours.
Impedance testing involves applying an AC current to the test plates via probes that are attached to the terminals. The internal impedance of the battery is measured in milliohms, with a higher reading indicating more deterioration. All major manufacturers give pre-defined thresholds, at which point they recommend complete UPS battery replacement.
Impedance testing is popular as it gives a general indication of the battery’s condition without negatively impacting functionality.
Regular impedance testing (at least twice a year) allows you to build up a detailed history of the battery condition for each cell. This will reduce the chances of battery failure and give you a rough idea as to when UPS battery replacement is required.
This form of testing is much quicker and simpler than other types. The main disadvantage is that it only gives a broad indication of condition rather than a detailed analysis.
Electro-Chemical Testing
This is another non-invasive type of battery testing. It involves using probes on the terminals, which measure the response to current/voltage signals that are passed into the battery. The results of these tests are cross-referenced against performance data from ‘healthy’ batteries. Common markers that are compared include sulphation and electrolyte dry-out.
Traditionally, electro-chemical tests were undertaken in laboratories to predict the likelihood of battery failure occurring on space vehicles or satellites, Nowadays, they can be used in a wide variety of contexts and there are portable hand-held testing units.
Because electro-chemical testing measures electrolyte dry-out and sulphation rather than merely impedance, it is believed to provide a more accurate and detailed picture of the battery’s condition. Any blocks that are identified as failing can be either be recharged at a higher rate in order to reduce sulphation or replaced entirely if necessary.
Load Bank/Discharge Testing
This type of testing is regarded as the most comprehensive and is, strictly speaking, the only type that determines the capacity of the battery string. This method is essentially an audit of the battery condition under both normal and peak loads. This test demonstrates which cells are able to hold their charge and indicates which ones may be nearing the end of their useful service life.
There are two main types of load banks that can be used for UPS testing: AC and DC Resistive load banks and reactive load banks. Both are effective in different situations.
Partial Discharge Testing
This type of testing involves discharging the batteries – but only up to 80%. This means that although they will be out of action, they should be available again within 10 hours. If there is a fault that needs the UPS to run off its batteries, it can do so, although only at 20% of full capacity.
UPS battery replacement When your tests indicate that your UPS battery is nearing the end of its service life, it is important to get the best new battery. UPS batteries vary in quality, but it is fair to say that those with a premium cost will generally provide better performance and last longer.
To summarise, UPS batteries can save the day in the event of a power cut, so regular testing and replacement (when needed) – are both extremely important.
