Battery Testing Methods · Last reviewed 2026-09-16
| Method | What it captures |
|---|---|
| Cycle-life testing | Fade from use — cycles to 80% capacity |
| Calendar-aging testing | Fade from time + temperature + state of charge |
| Resistance tracking | Internal resistance rise alongside fade |
The standard protocol fixes the conditions — depth of discharge, temperature, charge/discharge rates — and counts cycles until capacity reaches 80% of original, the conventional end of life. Because the result depends on those conditions, a cycle number without them is meaningless: the same cell can show wildly different cycle life at 50% vs 100% depth of discharge (see cycle life vs calendar aging).
A battery also fades while idle — faster in heat and at high state of charge. Calendar-aging tests hold batteries at controlled temperatures and charge states for months, mapping how quickly capacity and resistance drift without any cycling. The two aging paths run simultaneously in real life, so a lifespan claim needs both numbers, not just the cycle count.
Accelerated testing compresses years into weeks by raising temperature and cycle rate — which can distort the result, because the acceleration itself changes the chemistry. Real-world field data remains the ultimate check on accelerated predictions, which is why manufacturers update their life models as fleet data arrives.
My read: The cycle count on a datasheet is a promise under laboratory conditions — the honest lifespan number is the pair (cycle life + calendar aging), because a battery fades even while you are not using it.
Why I think so: Most quoted cycle lives omit their conditions, and almost all omit calendar aging. The buyer who asks for both — and the test conditions — is reading the lifespan claim the way it actually behaves, not the way marketing prefers.
My view as an editor, not a purchasing guarantee.
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