Start with the task
You usually want to know whether a cell is still useful — not a laboratory capacity curve.
Match the tool to the question: quick check, voltage reading, or real capacity for NiMH AA/AAA.
Household cells (AA, AAA, C, D, 9V)
A simple battery tester is enough for a good / low / dead reading on common household sizes.
A digital multimeter can show open-circuit voltage; that helps, but a tired cell can still read near-nominal voltage until loaded.
For rechargeable NiMH, a charger-analyzer that discharges and measures capacity answers “how much is left?” better than voltage alone.
Coin and button cells
For inexpensive CR / LR / SR cells, fitting a known-good fresh cell of the correct code is often simpler than testing.
If you do test, use a coin-cell tester or multimeter — and remember voltage does not make chemistries interchangeable.
After a “good” reading
If the cell tests fine but the device still fails, check orientation, contacts, and the model notes on the device page — the fault may not be the battery.