A battery that lasted a full afternoon indoors can report empty within an hour outside in winter. Very little of that energy has actually been consumed.
Chemistry slows before it stops
A lithium cell produces current through ions moving between two electrodes through a liquid electrolyte. That movement depends on temperature, and it becomes sluggish as the cell cools.
Slower ion movement shows up as higher internal resistance. The cell can still supply energy, but it cannot supply it quickly, and it sags under load in a way it never does when warm.
Cameras read voltage to estimate remaining charge. A sagging voltage looks exactly like an empty battery, so the body reports depletion while a substantial reserve remains chemically present.
Why the charge appears to return
Bringing the same cell indoors and leaving it for a while frequently restores several bars. Nothing has been added; the chemistry has simply recovered its normal pace.
This is the clearest evidence that cold causes a reporting problem rather than a consumption one, and it is why experienced operators do not discard a cell that failed in the field.
The recovery is not total. Repeated deep discharge at low temperature does cause real degradation, particularly if the cell is charged while still cold.
The camera makes the problem worse
Cold conditions raise consumption independently. Screens are run brighter against snow glare, stabilisation works harder, and the body may spend energy keeping components within operating range.
High frame rates and long recordings draw more current, which is precisely the condition a cold cell handles least well. Peak demand and reduced delivery arrive together.
Battery grips and external packs help mainly by adding thermal mass, which cools more slowly than a small cell sitting in an exposed compartment.
Warmth is the practical countermeasure
Keeping spares in an inside pocket close to the body preserves them at working temperature. Rotating a warm cell in and a cold cell out extends a shoot considerably more than carrying extras alone.
Charging should wait until a cell has returned to room temperature. Pushing current into a cold lithium cell plates metal onto the electrode and permanently reduces its capacity.
Condensation is the second cold problem
Moving equipment from cold air into a warm room causes moisture to form on and inside the body, including on contacts and the sensor stack.
Sealing gear in a bag before coming indoors lets it warm slowly with the condensation forming on the bag instead, which protects both the electronics and the battery contacts from corrosion.