A battery can enter a compartment and still be the wrong electrical or chemical choice. Equivalence is the result of four separate checks, not a measurement alone.
Four gates, one verdict
The physical gate compares diameter, height, shape and terminals. The electrical gate compares nominal voltage. The chemistry gate identifies the electrochemical system and whether the cell is primary or rechargeable. The drain gate checks whether the product is intended for the load pattern.
Only codes resolving to the same canonical family pass as exact equivalents. A mismatch does not always mean immediate physical incompatibility, but it prevents an unqualified replacement claim.
Three examples
LR44 and the SR44 pair share dimensions but differ in chemistry and nominal voltage. CR2032 and CR2025 share chemistry, voltage and diameter but differ by 0.7 mm in height. SR626SW and SR626W share size, voltage and chemistry but differ in drain designation.
Same size, different chemistry → conditional.
Same diameter, different height → not the same physical size.
Same size and chemistry, different drain suffix → conditional.
Device approval is a separate question
Even an exact family match does not prove that a particular brand, terminal version or product is approved for a device. Follow the device maker’s current instructions, especially for safety-critical or sealed equipment.
Physical compatibility has more than two numbers
Diameter and height are the main round-cell dimensions, but terminal form, cap shape, tabs and compartment contact design can also matter. A nominal dimension is not a promise that a modified or tabbed product fits an assembly.
A near-match can be too thin to maintain pressure, too tall to close safely or the wrong diameter for retention. Never modify a compartment or stack cells to manufacture a fit.
Electrical compatibility is not nominal voltage alone
Chemistry influences the voltage curve and behaviour under load. Drain designation adds another layer for watch cells. Rechargeability is a separate safety boundary: a primary cell must not be placed in a charging process simply because its shape resembles a rechargeable product.
A transparent outcome is more useful than “yes”
An exact verdict names one canonical family. A conditional verdict identifies the field that differs. A same-diameter verdict quantifies the height gap. An incompatible verdict names the material mismatch.
This structure lets a user take the remaining question to the device manufacturer instead of receiving an overconfident one-line answer.
Four-gate checklist
For each proposed substitution, write one line for physical format, one for nominal voltage, one for chemistry and rechargeability, and one for drain behaviour. A blank or uncertain field is not a pass. State which gate fails and what evidence would be needed to resolve it. This produces a useful answer without pretending uncertainty has disappeared.