Over the last 20 years the preferred battery choice for use in UPS are valve regulated lead-acid (VRLA) batteries. VRLA batteries have reduced installation and operating costs, have a smaller footprint and are lighter in weight with less environmental concerns than their counterparts. Although they are designated maintenance free, this does not mean they do not require any maintenance at all throughout their lifecycle.

Although they are generally reliable, batteries are quite complex electrochemical structures and as such can suffer from varying degrees of performance and reliability issues due to many factors such as temperature, frequency and duration of use, charging, manufacturing variance and quality etc.


Batteries can be configured in different ways depending on the requirement. They can be connected in series to make up a string and the number of blocks in a string will depend upon the required DC voltage of the UPS. The capacity of the battery determines the autonomy of the system (run time while on battery) and larger capacity batteries or additional strings connected in parallel will increase the autonomy. For highly critical loads, installing multiple strings is advisable to improve reliability and resilience, as a single faulty cell within a string could prevent that string being available when needed most.

Battery life expectancy is dependent on a number of factors such as frequency of use, duration of use, heat and humidity etc. As a result, all manufacturers recommend that batteries are periodically tested to ensure they are still functioning correctly. A UPS Health Check will include a reading of your overall battery capability.

Unfortunately it is a fact that UPS batteries won’t last forever. Battery manufacturers state a design life which indicates the length of time a battery will last when used under carefully controlled laboratory conditions. The battery service life is an indicator of the real life expectancy of a battery as it takes into account how the application, installation, operating conditions and maintenance all impact the battery. The service life is therefore a guide to when a battery should be considered for replacement and generally a 10 year design life battery will have a service life of around 7 to 8 years and a 5 year design life will have a service life of around 3 years given that it is well maintained and in optimum conditions.

The most common failures in a battery are grid corrosion and dry out. Grid corrosion (plate growth) can reduce the mechanical strength of the grid resulting in the internal resistance of the battery increasing and subsequently the capacity decreasing. Dry out is caused as a battery loses electrolyte over time. While conditions are optimal with the temperature kept constant around 20°C the loss of electrolyte will be gradual. In higher temperatures however this loss is accelerated and a 10°C increase in temperature can reduce the life of the battery by half. Other failures can also occur such as electrolyte leakage, thermal runaway, cell reversal etc. but grid corrosion and dry out, account for up to 80% of common failures occurring. With a good battery maintenance program, P & I engineers can predict your battery performance and help prevent any premature catastrophic failure before it occurs.

P & I can offer complete battery maintenance and testing programs and as required supply and install replacement batteries for all UPS makes including AEC, APC, Eaton Powerware, Emerson (Chloride, Liebert), GE Digital Energy, MGE, Riello, Salicru, Socomec and many more.

Please contact our service team who will be happy to assist.