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You charge it, it glows for weeks, and then, with no drama at all, the flame sags to a half and the warm white you bought now reads as a tired amber. You assume the LED is dying. It isn’t. The cell inside is.
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The Cell, Not the Light, Is the Timer
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Every rechargeable LED candle runs a small lithium-ion pack, and its usable capacity decays by calendar and by cycle, whichever hits first. A 3.7V single cell that ships at 100 percent is at the mercy of two curves: the number of full charge-discharge cycles it has run, and the average voltage it sits at on the shelf or in the drawer. Modern cells are rated roughly 300 to 500 full cycles before they dip below a usable floor, but the real killer is deep discharge. Every time the candle runs down to the point where the flame flickers to death and you forget to charge it for weeks, you are letting the cell park at 3.0V, the voltage where the lithium oxide lattice slowly sheds its stored lithium. That shed lithium is gone for good. It is not a calibration quirk. It is electrochemistry spending your light.
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Three Numbers That Predict the 90-Day Drop
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- 300-cycle rating. Most budget candle cells are spec’d to 80 percent of original capacity after 300 cycles. If your candle is used hard, that is roughly eighty to a hundred days of evening use. The fade you are blaming on the LED is the pack’s capacity curve, delivered on schedule.
- The 3.3V floor. Below about 3.3V on a 3.7V cell, internal protection kicks in and the board refuses to drive the LED to full brightness. The candle does not die — it simply refuses to shine, which is what feels like death. A top-up charge before it hits the floor is worth ten times more than an overnight charge after.
- Storage voltage. A cell left at full for months ages faster than one stored near 4.0V (about 60 percent). If the candle spent a season in a drawer at 100 percent, it gave away capacity while you were away.
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Run the Charge Regime, Not the Luck of It
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- Charge before the sag, not during it. Top up at half brightness, not at the last flicker. You are trading a deep, damaging dip for a shallow, harmless one.
- Mind the heat. A candle left charging on a sunny sill or near a lamp runs hot, and lithium ages at heat. A cool surface, a short top-up, is cheaper than a full overnight cycle at 28C.
- Rotate the units. In a set, alternate which candle is on the table. Splitting cycles across a battery means the whole set stays above the fade line together instead of collapsing in sequence.
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Battery life is a chemistry you manage, not a warranty you wait out. If the cells are the limit, buy ones built with capacity headroom and honest cycle ratings at YSCandle — light that holds its glow for the whole room, not just the first evening.
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Recommended LED candles for this use case: