Your car key fob may start needing several presses to unlock the door, and an AirTag might stop responding when you try to locate it. Before assuming the devices are at fault, check the battery inside. A common type is the CR2032, a 3‑volt lithium coin cell also used in Samsung’s SmartTag 2 and various smart‑home sensors. Depending on usage, it can last well over a year. A digital multimeter is the most reliable tool for measuring its voltage, though there are cheaper methods. Keep in mind that voltage alone does not give a complete picture of battery health.
**Testing a CR2032 with a multimeter**
First, inspect the battery for any crusty residue, rust‑colored patches, swelling, or leakage. If you see any of these signs, discard the cell and replace it. Also look at the device’s contacts; corrosion there can cause problems even with a good battery.
Remove the CR2032 and set your multimeter to DC voltage (the symbol with a solid line over a dashed line). Connect the black lead to the COM jack and the red lead to the V or VΩ jack. If the meter does not auto‑range, choose a setting above 3 V, such as 20 V.
Place the battery on a non‑conductive surface and hold it by its edges. Touch the red probe to the larger face marked with a plus sign (+) and the black probe to the smaller, flat side underneath. Keep the probe tips from touching each other. A negative reading simply means the probes are reversed.
A fresh CR2032 typically reads close to 3 V. A reading near 2.5 V suggests the battery should be replaced. However, a multimeter draws almost no current, so a battery that measures 3 V may still struggle when the key fob or tracker demands power. There is no universal pass‑or‑fail voltage for every device. If the gadget continues to misbehave, try a new CR2032 before concluding the device is defective.
**If you don’t have a multimeter**
A dedicated coin‑cell tester is an alternative; some models cost about $10, though many only measure voltage and not performance under load. Basic multimeters can be found for under $20 and are useful for checking other batteries and low‑voltage electronics. Buying either tool solely to diagnose a $3 battery may not be cost‑effective.
Another low‑tech option is the LED test. Use a small red or yellow LED, which requires less voltage to light than blue or white LEDs. Connect the longer leg (positive) to the battery’s positive side and the shorter leg (negative) to the opposite side. If the LED lights, the battery can supply some current. This test only confirms that the cell can deliver a small load; it does not indicate how much life remains, and a dark LED does not guarantee the battery is dead.
AirTag owners can also check battery status in the Find My app. Open the app, select Items, tap the AirTag, and look for a “Low Battery” warning or a depleted‑battery icon. If either appears, replace the CR2032 without further testing.
Some CR2032 cells have a bitterant coating that can impede contact even when new. Apple advises using batteries labeled “Compatible with Apple AirTag” for replacements and notes that an AirTag’s battery lasts more than a year. Samsung rates the SmartTag 2’s battery life at up to 500 days in normal mode.
After removing a CR2032, keep it out of reach of children and tape over its terminals before taking it to a battery‑collection facility. If a battery is swallowed, seek emergency medical care immediately, as serious internal injuries can develop within two hours.