Because the gauge estimates rather than measures, and an aged cell holds a high voltage briefly before collapsing under load. A published shot count describes a new cell, not the one in your hand.
A camera battery gauge is an estimate presented as a measurement, and the estimate degrades with the cell.
What the gauge is doing
Reading voltage and inferring capacity. That inference relies on a discharge curve which shifts as a cell ages: the resting voltage stays respectable while the ability to hold it under load falls away. The camera therefore reports full, then drops several steps at once when the shutter or the screen draws current.
Why the published figure does not help
A shot count is measured to a defined procedure with a new cell. It says nothing about a cell that has been through two hundred cycles, and nothing about cold — and no listing in this catalogue publishes a capacity at a stated low temperature.
What to do
Carry spares and rotate them, rather than trusting a gauge. Battery grips — thirteen products here — hold additional cells rather than extending the life of one, which is the distinction worth knowing before buying either.
When to retire a cell
When it can no longer finish a session it used to finish. There is no published threshold, and the absence is itself the finding: this is a judgement from your own use, not a specification.
What people ask before they commit
Is the gauge simply wrong?
It is doing something harder than it appears: inferring remaining capacity from voltage under load, on a curve that shifts as a cell ages. A worn cell sits high on that curve at rest and falls off it quickly once the camera draws current — which reads as full, then empty, with little in between.
How do I tell an aged cell from a faulty charger?
By swapping one at a time. A second cell that behaves the same on the same charger points at the charger; the same cell failing on two chargers points at the cell. Neither test needs a figure, and no listing publishes a cycle count that would answer it directly.
Last reviewed 12 September 2026