How Do I Know a Battery Is Aging? Is Capacity Fade Normal?

Yes, gradual capacity fade is normal. Every rechargeable lithium battery loses a small fraction of its useful capacity over time as active material degrades and internal resistance grows. The real question is whether the fade follows an expected curve or signals premature failure.

Visible signs of aging

The most practical sign is shorter run time: a fully charged battery no longer lasts as long as it did when new. Under load, the voltage sags lower and recovers more slowly, and the cell may run warmer than usual at the same current.

Measuring the underlying changes

Bench tests show two trends. First, the measured capacity after a full charge gradually declines; under typical use, healthy cells still retain a useful portion of capacity after hundreds of cycles. Second, internal resistance rises, increasing heat generation and reducing usable power.

When fade is abnormal

Sudden drops, swelling, overheating during charging, or a failure to hold charge after only a few months suggest a manufacturing defect, misuse or an unsafe condition rather than normal aging. Such packs should be inspected or replaced promptly.