Risk management in batteries for medical (and other) applications

A battery is a corrosive device that begins to fade the moment it leaves the assembly line. Battery failure is common, and up to 50% of system breakdowns are attributed to a failing battery. Much of this is avoidable, but even with the best of care, some batteries die early and scientists don’t know why. Batteries exhibit human-like characteristics and the health rests on the genetic makeup, environmental conditions, and user pattern.

The manufacturer specifies the run-time of a device on a battery performing at 100% capacity, but most operate at less. As time goes on, the performance declines further, and the battery gets smaller in terms of storing energy. Most batteries deliver 300 to 500 full discharge/charge cycles, more on a partial discharge.

In the first year, most batteries work well, but the confidence fades in the second and third year. As batteries begin to lose capacity, new packs are added and in time, the battery fleet becomes a jumble of good and failing batteries. This is when the headache begins. Unless date stamped or other quality controls are in place, the user has no clue about the history of a battery, much less its performance.

The energy in a battery can be divided into three segments: available energy, the empty zone that can be refilled, and the unusable part or “rock content” that has become dormant.

The “ready” light on a charger can’t verify a battery’s “health.” Ready only reveals that the battery is fully charged. As the active space of a battery declines with age, charge times also decrease. Many battery users are unaware that weak batteries charge faster than good ones. The low performers gravitate to the top and become disguised to the unsuspecting user who trusts the “green light.” A short charge time is not only reserved to a poor battery, a pack with a partial charge also charges quickly because there is little to add.

A battery needs constant care and feeding. Even if fully charged, self-discharge consumes valuable energy. This is not a manufacturing defect but a battery characteristic, although poor manufacturing and improper handling can elevate the problem.

This article examines battery issues such as “care and feeding”, self discharge,  and service issues such as incoming inspection, periodic capacity check, and even retirement. To read the article, which appeared at Medical Electronics Design, click here.

About the author

Isidor Buchmann is the founder and CEO of Cadex Electronics Inc. For three decades, Buchmann has studied the behavior of rechargeable batteries in practical, everyday applications, and has written articles and books, including “Batteries in a Portable World.”

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