An end-of-life indicator (EOL) is a feature on a quartz watch that warns you the battery is about to die. Instead of stopping without notice, the watch changes how the seconds hand moves so you know it's time for a new battery.
How it warns you
The most common EOL signal is the seconds hand jumping in four-second steps instead of ticking once per second. When you see the hand hop every four seconds, the battery has only a short time left — usually a couple of weeks. It's the watch's way of giving you fair warning before it quits.
Why it exists
A dead battery that stops silently can leave you wondering whether the watch broke. Worse, a battery left dead in the case too long can leak and damage the movement. The EOL feature protects you on both fronts: you get a clear signal to swap the battery, and you're nudged to remove the old one before it leaks.
Which watches have it
EOL is a quartz-only feature — mechanical and automatic watches have no battery, so they don't need it. Most quality quartz movements include it, but cheaper ones may not. If your quartz watch suddenly starts moving in four-second jumps, nothing's wrong. It just needs a fresh battery.