Simple battery tester
Best for: a fast household check (AA, AAA, C, D, 9V; some handle coin cells).
Answers: broadly good, low, or dead under a light load.
Limits: often crude; may not measure capacity; not a substitute for the correct chemistry.
Digital multimeter
Best for: measuring voltage and general electronics work.
Answers: what voltage the cell is producing at rest (open-circuit).
Limits: a “good” voltage can still hide a weak cell under load; you must know the expected voltage for that chemistry (about 1.5V alkaline, about 1.2V NiMH, about 3V CR lithium).
Charger-analyzer
Best for: rechargeable AA/AAA you reuse often.
Answers: usable capacity (mAh), and can refresh or cycle cells depending on the unit.
Limits: not for disposable CR coin cells; only useful when the device actually supports NiMH.
Quick pick
Unsure if the AA in a remote is dead → simple tester or multimeter.
Managing a set of NiMH for a GPS → charger-analyzer.
CR2032 in a tracker → usually replace with the correct code rather than over-investing in testing.