How Often Do I Replace Lead Acid Backup Batteries?

Lead acid batteries are still the standard battery used in a wide variety of backup power applications, from backup generators to uninterruptable power supplies (UPSs) to emergency lights to security panels.

How often you replace your batteries depends on how business critical or life critical the systems the backup power is protecting. The general rule of thumb for business critical systems is 3 years – backup generators, UPSs, emergency lighting, and so on. Organizations with large fleets of batteries, such as backup generators deployed across many buildings on a campus, schedule a rotating subset of batteries to change each year.

Maintenance Goal Battery Replacement
Life Critical 2 years
Business Critical 3 years
Before The Battery Fails 4 years
Don’t Give a Damn 5 years

For life critical applications, such backup power used in medical situations, you may go as often as every 2 years. In this scenario you are replacing batteries before any significant degradation or chance of failure occurs.

On the other end, run-time starts to degrade as batteries degrade in the last several years of their service life. 4 years is about as long as you go if you can live with degraded battery life and want to avoid an out-and-out failure. At 5+ years you pretty much don’t give a damn, and likely will experience backup power failure. Additionally, the sealed lead acid (SLA) batteries used in uninterruptable power supplies(UPSs) swell when they fail at end of life. In mid-sized UPSs, this swelling makes the batteries impossible to remove from the UPS, ending the UPSs life as well.

When Sealed Lead Acid (SLA) batteries fail after 5 years, they overheat and swell. At this point they are too large to be removed from the unit, other than by extra-ordinary means.

Lithium ion batteries are coming to back up power. They are arriving first in UPSs, such as described by APC here. APC describes the benefits as:

  • Doubling battery service life to 5 years
  • Allowing for a 5 year warranty on both the UPS and the battery
  • Better high temperature performance
  • Lower weight
  • Lower cost of ownership (but with a higher up front price)

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