By Roy Gates, Saft America, North Haven, CT

While reviewing an old battery instruction manual, it brought to mind the simpler days of battery installations, the last page merely said, “Congratulations, this battery’s life is now in your hands.” The manufacturer was highlighting the fact that batteries are living “beings” with a life cycle, personalities and quirks all their own.

Giving a stationary battery the right start in life sets the tone for its dependability when called on to do its job. Proper care and feeding throughout its life eliminates unwanted experiences as it ages, and helps predict when the aging process begins pointing toward a planned, cost-effective replacement.

Proper Battery Testing at Installation

But just what testing is required, how often should it be performed, and who is responsible? Once the data is collected, owners and installers are faced with the challenge of what to make of the results.

The maintenance and testing work performed during the battery installation, when accurately recorded and carefully reviewed over time, greatly increases the reliability of an emergency power system. Let’s review the “musts” and “shoulds” of various stand-by batteries, and how cutting corners leads to lost time and revenue for the owner and installer.

 Is it true that all batteries are created equal? Well, sort of, kind of… No! While the concept of the energy storage device is consistent across a wide array of electro-chemistries, their operating characteristics and maintenance demands are somewhat unique.

Receipt, Inspection and Storage

Ideally, the standby battery should be delivered to its new home just before its scheduled installation. At the time of delivery, any spills, leaks or anomalies should be promptly reported to the carrier and manufacturer for remedy – this includes looking at the electrolyte levels, jar to cover joints, and inspecting for stresses on the cell cases themselves. Overlooked problems at this stage invariably become the “result of mis-handling during installation.”

The correct number of battery cells and model numbers should be verified. For the installer, this is the best time to take individual cell voltage readings. If the manufacturer’s final inspection procedure includes numbering the individual cells, follow their number sequence so the field data coincides with the factory inspection data (i.e. cell number 24 in the field is the 24 th test reading on the factory report).

This small, seemingly innocuous exercise carries a lot of weight with the battery manufacturer, and demonstrates good decision making on the part of the owner to hire you to install the battery. Consider the results of these readings the initial vital signs of the battery and when the commissioning, or start-up, is done – a new battery is born.

Next, the installer should locate and record the last charged information on the cells or packing material. All batteries that are delivered filled and charged will need a refresher-charge at some point. The following table gives general guidelines for safe open circuit storage, at various temperatures.

 

Battery Design	50 o-75 oF	75 o-100 oF
Filled, Vented Lead Acid	3 – 4 months	1 – 3 months
VRLA	3 months	1 month
Ni-Cd	6 – 12 months	3 – 6 months

A noted exception to this rule is certain nickel cadmium (Ni-Cd) cells that can be delivered filled and discharged.

Of course, local filling before installation affords more flexibility in storage times, but present other, unique challenges for the installer. Consult with the manufacturer quickly in the entirely unlikelyevent the installation will be delayed longer than the recommended storage time. Nipping this issue in the bud ensures a better installation for the battery, and clearly determines who has liability for a less than stellar commissioning and start-up, and may eliminate one reason for the owner to enforce their payment retention rights.

Starting Out Right

Assembling the cells into a battery (either on an open rack or into an enclosure) is relatively uneventful, as long as technicians observe good safety practices – no open flames, smoking, sparking, arching, and the use of non-insulated tools is highly recommended.

While the battery is on open circuit (not charging or discharging) very little hydrogen gas is emitted from the cell, so the risk of detonation is minimal. However, batteries are stored energy devices, and bridging the terminals of a cell, or group of cells, unleashes DC currents from 10 to 30 times greater than the nameplate ampere-hour (Ah) rating of the cell.

A shorted terminal at best results in the need for a change of clothes, and at worst sends shrapnel of lead pellets from the terminal post, causing permanent damage and exposing the technician to dangerous current flow, possibly causing serious injury.

Once the cells have been installed, connected properly (please follow the manufacturer’s torque rating for the hardware), and are ready to begin their life, verify the appropriate DC buss voltage is present, and connect the batteries to the charging source. Recording the cell voltages prior to charging helps to demonstrate storage has been in accordance with the battery maker’s recommendations.

Finally, consult the installation manual or card to properly commission the battery. This is the real birth of the battery as far as the owner is concerned. Making sure the first charge is done properly eliminates many operational problems down the road.

To Ohm or Not to Ohm

It is wise to take advantage of today’s modern ohmic measuring devices to validate the connections are clean and tight, and the internal resistances of the cells to ensure they are within manufacturers’ guidelines. This is especially true for valve regulated lead acid (VRLA) batteries, but is applicable to vented lead acid cells as well. Internal ohmic readings have little benefit on nickel-cadmium (Ni-Cd) battery installations as their internal components are not susceptible to corrosion, and the electrolyte remains at a consistent density.

 

So at the beginning of the battery installation life, you should be able to deliver to the owner:

• “As received” reports, including cell voltages and details of the visual inspection,

• Any re-charge or re-freshening work performed, and

• Pre and post commission-charge cell voltages, specific gravity readings, connection resistance, and internal cell resistance.

 

You may ask, is it really worth it to perform these additional inspections? In a word, YES. As a battery manufacturer, I can confidently say the majority of trouble-shooting calls we receive are a result of either poor start-up commissioning of the battery or shoddy record keeping.

Most battery fabricators today employ automated, precision manufacturing practices and have many inspection points in the process. The final testing and inspection carried out at the factory is our last seal of approval, and well, most manufacturers will testify the battery was in great health when it left the factory, so something (prolonged storage, improper installation, poorly performed or omitted commissioning) happened along the way, resulting in either a bad cell or test result. Overwhelmingly, the absence of records results in denial of warranty claims. Do you want your customer hearing us saying it was your work that concluded with a bad battery?

How’s Everything Going?

The life of the battery is now in the hands of the operator. What they do with it can range from nearly nothing, to diligently following the recommendations of IEEE Maintenance guidelines:

• IEEE 1106 – Maintenance and testing of Ni-Cd batteries.

• IEEE 450 – Maintenance and testing of vented lead acid batteries.

• IEEE 1188 – Maintenance and testing of VRLA batteries (yes, an entire maintenance guide to the “maintenance free” battery).

For years, battery maintenance revolved around checking the battery visually, reading and recording voltages, monitoring electrolyte levels and periodic specific gravity checks. While these staples of battery care remain useful today, more sophisticated methods of monitoring battery health are growing in popularity, and companies dedicated to battery maintenance continue to sprout up.

So, How Much Testing is Enough?

As noted above, industry standards exist to consolidate the best ideas of manufacturers of batteries and test equipment alike, and include a dose of owner reality too. The owner has a myriad of choices to accomplish these tests. The savvy electrical contractor, who can specialize in battery diagnostics as well as installation, can become the trusted advisor to battery users.

Many manufacturers offer their services as well, which many times carry the benefit of warranty validation and streamline that ever-painful process. Always an option, the owner can carry out the maintenance and testing themselves.

Is there an investment in getting the job done right? Absolutely. But the biggest investment is manpower and devotion to the maintenance program. Hence, outsourcing the testing at least seems to be more and more common.

So What of These Tests?

Starting with the basics, individual cell voltage readings should be taken periodically (see table for frequency). To ensure the charger setting has remained constant, measure the battery voltage at the main positive and negative terminals of the battery; do not use the voltmeter on the charger, as you need to account for voltage drop in the cables and these meters are typically accurate to approximately two percent.

 

Battery Design	Overall Battery Voltage	Pilot Cell Voltage	Individual Cell Voltage
Vented Lead Acid	Monthly	Monthly	Quarterly
VRLA	Monthly	Monthly	Quarterly
Ni-Cd	Quarterly	Quarterly	Semi-annually

 

A digital voltmeter should be used; one that logs the cell voltage and downloads to a spreadsheet is even better. The overall battery voltage should be recorded, and should be the sum of the recommended cell voltage multiplied by the number of cells in the string.

Individual cell voltages should be within a given range of each other, typically 30-40 mV (consult manufacturer for recommendations) and within 5-10 mV of the per cell value recommended by the manufacturer. Voltage testing should be done with the battery connected to the charger and with the charger turned on. This maintenance practice applies to all stationary battery designs in service today.

The corrective action(s) for cell voltage imbalances includes equalize charging (i.e. boost or high-rate charging), individual cell charging, or further investigation via reference electrode testing.

Reference electrode testing is a specific measurement of each plate’s (positive / negative) potential against a known, third electrode, immersed in the electrolyte. For lead acid batteries, particularly lead calcium designs; this is a useful test as it is quite common for the negative polarization to vary more than -100mV from cell to cell. What is important is that the positive plate has a polarization of +80-100mV. A positive polarization that is too low means the positive plates are under-charged, and a polarization that is too high results in excessive gassing and accelerated grid corrosion.

For vented lead acid cells, annual specific gravity readings are useful for diagnostics in case of a problem. Cell voltage readings or specific gravity readings are NOT an indication of the battery’s available capacity, but rather offer a snap shot of the battery’s state of health at this particular time. Hence, these tests should be performed at regular intervals to provide a trending result.

Even Better

The natural aging process of lead acid batteries is corrosion. Corrosion leads to increased resistance (or conversely decreased conductivity) with the result being impeded current flow into the battery (flow of energy to be stored) and out of the battery (available performance of the electrode assembly).

Digital low resistance ohmmeters (DLRO) are used to quantify the actual resistance (typically micro-ohms) within the cell, and today, test apparatus is available designed specifically for obtaining these values from stand-by batteries. The more advanced testers allow the user to pre-program an acceptable range for the cells being tested, log all the information, and deliver a report highlighting cells that exceed the pre-determined limits.

The important rule to recognize with internal ohmic testing is that the best data comes from obtaining a good baseline, ideally at the start of the battery’s service life, and adhering to a regular test schedule in order to compare the readings over time.

As alluded to before, some test equipment measures impedance to an AC signal, others track conductance of the AC signal, while others measure voltage drop to a DC load applied to the cell, thereby calculating actual resistance. Ensure the readings are obtained with the same type of apparatus each time to maintain consistent readings.

Some Important Distinctions

Internal ohmic testing has great predictive value in determining the state of health of VRLA batteries. Owing to their “black box design,” there are few routine maintenance practices that offer as much insight into changes occurring within VRLA cells. Consequently, IEEE 1188 recommends quarterly internal ohmic testing of all cells / units in the battery string. In addition to assessing grid corrosion, internal ohmic testing captures the conductivity of the electrolyte.

 

Battery Design	Internal Resistance	Connection Resistance
Vented Lead Acid	Semi- Annually *	Annually
VRLA	Quarterly	Annually
Ni-Cd	Not Applicable	Check cable connections annually

* For abusive conditions – internal ohmic measurements can be done annually when the battery is in a good operating environment

With regard to Ni-Cd batteries, there is little change to resistance of the electrode stacks as the plates are constructed of steel and immersed in a potassium hydroxide electrolyte, which acts as a preservative to the steel. Ohmic type tests will highlight short-circuited cells. Finally, while internal ohmic testing is a very useful tool in determining how gracefully the battery is aging, there remains much work to be done to confirm actual capacity of the battery by this type of testing.

So just how do you determine how much capacity remains? Good question, glad you asked. Hopefully, all battery installations were given careful consideration as to what size battery is required, and whether the application demands very high currents for brief durations (UPS, engine cranking), or low, steady current supply over long periods of time (photovoltaic, remote telemetry), or a combination of both (substation switch-tripping, turbine applications).

The ideal test to validate the battery’s ability to do its job is to evaluate the battery as it performs the duty cycle. But this isn’t always practical (varying load currents, duration of the run time, etc.). Performance or modified performance tests are done to compare the original performance data to what the battery can deliver in its current state. While you may not be able to mimic the actual duty cycle for which the battery is intended, it pays to ensure the modified tests do correlate to the battery design installed (may require revising).

Batteries engineered for high current loads for short duration should be tested with higher currents for shorter periods of time. Testing a 10-minute lead acid UPS battery at a three-hour published rate may not accurately reflect the impact corrosion has had on the current delivery structure within the plates.

The same holds true for low rate discharge batteries – they were chosen to supply a low current for some length of time – a rapid discharge test may result in artificial failure results.

Both the battery manufacturers and IEEE share the following philosophies:

• Prepare the battery for discharge testing by correcting known deficiencies (low state of charge, dirty or loose connections) so the test reflects the battery’s condition, compared to new.

• Omit preparing the battery for test and understand that the results may lead to remedial action by the owner to correct less than adequate conditions, and the battery should be re-tested to verify it the battery is nearing replacement or improved / additional maintenance practices are needed.

 

As the owner, make certain your requirements for performing discharge testing are clearly outlined. As a testing contractor, understanding the battery’s intended service increases the value of your work and the confidence the owner should place in your organization. It does not take that much more time to qualify the appropriate test for a given installation.

 

Discharge test regimes should follow the following guidelines:

Battery Design	Acceptance test	Periodic Test Interval	Threshold for Replacement
Vented Lead Acid	Yes	5 years until degradation increases	Capacity falls below 80%
VRLA	Yes	Annual until degradation increase	Capacity falls below 80%
Ni-Cd	Yes	5 years	Since degradation is linear, replacement should be considered when the battery no longer satisfies the owner’s requirement (run time, end voltage, etc.)

It has been bantered about that discharge testing uses up battery life. This is not exactly accurate. The majority of today’s stationary battery designs can easily withstand the number of discharge outlined above. Avoiding useful discharge testing because of this fear is unfounded. Discharge testing can be time consuming and costly, but it remains the best measurement of the installed battery’s health.

Finally, some last words on oft overlooked indicators of battery health. Temperature plays an enormous role in the life and performance of a battery. Low temperatures reduce the available current that can be drawn from the battery and must be taken into account when sizing the battery.

High temperatures (>80 oF) accelerate the aging process, thereby reducing the useful service life. The amount of life lost can be determined through the Arrhenius equation, and the industry rule of thumb is 50 percent life loss for every 15 degrees Fahrenheit a lead acid battery operates above 77 degrees Fahrenheit. Ni-Cd batteries experience roughly 20 percent life loss under the same parameters.

In consideration of VRLA batteries, temperature monitoring is very important. Their internal recombination of the gasses produced by the plates is exothermic in nature; hence they tend to operate slightly warmer than the environment they are in. Abnormal deviations in block temperature (measured at the negative terminal post) from ambient of roughly five degrees Fahrenheit or more are good indications the VRLA battery health is deteriorating and remedial action is imminent.

Another excellent indicator of battery health is the amount and stability of float current the cells require to maintain their set voltage. Unfortunately, high-resolution ammeters are rarely used in battery maintenance practices, but if they were, users and test technicians could accurately predict pending replacement needs by trending increases in the current demanded by the battery.

Now that the battery’s life is in your hands, I hope you will agree there are several useful methods to plot its aging and performance. The most important aspect of battery testing is that it be done safely, and consistently so the information obtained and reviewed can instill confidence in the emergency power system, and accurately predict the appropriate time to schedule the replacement of an aged, well-used friend.

 

Author Biography

Roy Gates is the Director of Sales for Saft America’s Industrial Battery Group (IBG). He has been with Saft for 18 years with responsibilities that included installation and service work, educational seminars, and sales training / management. He has an electrical background, and was a residential / commercial electrician.

 

References

IEEE 450 – 1995 - Recommended Practice for Installation, Maintenance, Testing and Replacement of Vented Lead Acid Batteries for Stationary Applications.

IEEE 1106- 2003, Recommended Practice for Installation, Maintenance, Testing and Replacement of Vented Nickel Cadmium Batteries for Stationary Applications.

IEEE 1188 1997 - Recommended Practice for Installation, Maintenance, Testing and Replacement of Valve Regulated Lead-Acid (VRLA) Batteries for Stationary Applications.