Your UPS service provider has told you that you should change your batteries in your UPS to ensure continued reliability. You know these service technicians and their company have always treated you well and have not ever tried to add extra charges or work. So why are they saying your 5 year old batteries (which have a 10 year ‘design’ life) need changing?

What is a Battery?

A device that uses chemical means to store and deliver electrical energy. They can be found in any number of shapes, sizes, voltages and capacities. In UPS system applications they are typically Lead-Acid, either flooded or valve regulated (VRLA – sometimes called maintenance free – which means they don’t need water added). Most of the valve regulated batteries used in UPS applications have a design life of 10 years.

This discussion is based upon VRLA Batteries, though many of the discussion points also apply to flooded batteries, with the biggest difference being design life (typically 20 years for flooded)

Design Life versus Actual Life (ideal world vs. real world)

Design Life; hmmm…Ideal Circumstances, no discharges outside of specification, not repetitive, always occurring after the battery has had the correct amount of time to recharge to perfection, and of course always in a perfect environment etc.

Actual Life; well let’s talk about that…There are several factors that need to be understood as we go. Since batteries are an electro-chemical device they have a finite useful working life and left in service long enough, they will fail. How the batteries are used, the environment in which they are kept and the maintenance performed on them all effect the useful working life of the battery.

Temperature / Environment

Most manufacturers of VRLA batteries recommend a battery operating temperature of 70° F to 77°F and warn that any temperature excursion will shorten battery life (higher temperature) or limit actual performance (lower temperature). It is important to note that for every 15°F above 77°F the life of the battery is reduced by 50%; so if the ambient temperature in your application is 92°F your battery design life is already cut in half.

It is also expected that the batteries will be kept in a clean dust free environment as well.

Discharging / Charging (Cycling)
The batteries are used to provide power, through the UPS inverter to your mission critical loads in the event of a utility power disturbance. Typical application is a battery sized to provide 100% UPS load for 15 minutes, though this can change dependent upon the size of the UPS, whether there are generators available etc. Realistically however, how many UPS’s are actually loaded to 100%? And how many times are battery discharges exactly 15 minutes?

Every time the battery is discharged and then recharged (discharge / recharge cycle) a little bit of its overall life expectancy is used. Depth of discharge (how long and at what load) and frequency of discharges effect the batteries differently, and all contribute to length of useful life. Likewise so does the charging portion of the cycle (how often and for how long.) Batteries are DC power storage devices and require being charged with a DC voltage, however UPS are fed from AC. They rectify the AC to DC, then filter the DC to produce a good DC source, but it is not perfect and there is always a small amount of AC voltage present (AC Ripple) on the DC Voltage; the more AC voltage present the quicker the battery reaches end of life…this is one of the reasons that DC Filter capacitors are so important.

As stated earlier, each battery only has a finite useful life, cycling (amount and depth) effects the capability of the battery, and once the battery can only deliver 80% of its original capacity it is deemed to have reached the end of its useful life.

Maintenance

Batteries require maintenance. Battery maintenance is critical to the performance and reliability of your UPS. As discussed, batteries are electro-chemical devices, and as such their performance capability will deteriorate over time, even if not used. Monitoring is capable of showing this deterioration trend, but monitoring alone does not replace periodic preventive maintenance inspections and testing.

The primary objective of a battery maintenance program is to verify general health and indicators for proper support and capacity delivery. Effective maintenance must be regular, comprehensive and consistent including; visual inspections, temperature measurements, impedance/ conductance testing, voltage recording, as well as capacity testing (when appropriate) to identify any performance related issues.

So while not every site or actual usage is the same, as you can see, battery useful life is not the same as design life.

Learn more about Jantech Services Battery maintenance Options