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Battery Capacity (Load) Testing

What is Capacity (Load) Testing and why is it important?

Load Testing

No matter the type of backup system you have, an unplanned power outage is no time to find out that your battery won’t perform.

When a critical power system goes down, it’s often because of the condition of the battery system.  Conducting preventative battery maintenance according to IEEE standards (taking voltage & internal ohmic values) is always recommended.  But you cannot calculate a battery system’s available capacity (runtime) from these static readings.

Here are some basic battery capacity testing facts:

  • Capacity testing does not harm your battery.  This should not be a reason to not cap test your batteries.
  • Capacity (Load) Testing is the only way to calculate how much runtime is left in a battery system
  • You cannot calculate how much runtime is left in a battery from static readings (i.e. voltage, internal ohmic values or specific gravity)
  • When following IEEE testing guidelines, only a small fraction of the battery’s life is used when cap testing.  (i.e. VLA’s are typically warranted for over 120 full discharges.  VRLA’s are usually warranted for 25+ full discharges. These values can vary by manufacturer, discharge duration, temperature, application and other factors.)
  • Capacity testing helps protect the battery’s factory warranty and is often required by insurance policies
  • Capacity testing is recommended by IEEE upon installation, then  again in the first two years of service.  After year two, testing should not be greater than 25% of the expected service life.
  • Any battery that degrades to 85% of its service life, or less, should be capacity tested annually.

Importance of Capacity Testing

Learn why capacity (load) testing is so important.

Battery maintenance (collecting voltage and resistance values) is like a doctor doing a physical on you.  Capacity testing a battery is similar to getting on a treadmill and doing a stress test to prove how well your heart performs.  It’s the only way to see how much capacity you have left in a battery.

Your physician can listen to your heart and other vitals (similar to battery maintenance – monitoring battery voltage and internal ohmic values), but without putting you on a treadmill and watching how your heart performs under normal working conditions, he cannot guarantee the condition of your heart (battery).

A battery load test is like a cardiac “stress test”. Your battery is an electro-chemical device, that needs to be tested regularly to verify its capacity and determine if it will support your critical load during a power outage.

BCT Screen Shot

While periodic preventative maintenance is very important (and can point out gross battery issues) it cannot prove how long your battery will run when called upon when your utility power is interrupted.  Planned capacity (load) testing is the only way to verify the capacity of a battery.

We encourage periodic load testing as a portion of a comprehensive battery maintenance program. The IEEE recommends load testing upon installation (commissioning) and periodically thereafter (depending on the service life of the battery).  Summit Power follows all IEEE standards.

Our staff has the experience, expertise and equipment to efficiently load test your battery system. We capture the data needed to assess your battery’s condition and capacity (runtime) left.  A comprehensive cell by cell analysis report is provided to each client with any necessary recommendations.


For more information on battery capacity testing, contact us.