Rapid clicking
A fast tick-tick-tick-tick when you turn the key or press start is the classic low battery sound. The starter's solenoid pulls in and tries to engage. The battery's voltage sags under the load, the solenoid lets go, the voltage recovers, and it tries again, several times a second.
So the clicking isn't a broken part. It is what a battery with too little charge sounds like. If the dash lights also dim or flicker while you try, that points the same way.
It also doesn't mean the battery is ruined. A battery drained by a light left on overnight clicks exactly like one that is worn out. The sound can't tell you which you have, and that is the question a jump start helps answer.
One click, then nothing
A single click is less clear. It can still be the battery, if it is too far gone to try more than once. More often, when the dash lights stay bright while you turn the key, the battery is delivering and the trouble is further down the line, in the starter motor or its wiring.
A starter often gives some warning before it quits: a hesitation, or a day when the car only started on the second try. If that sounds familiar, the starter is more likely than the battery.
The headlight check
Turn the headlights on, then try to start the car while you watch them. If they dim a lot or go out, the battery or a poor connection is the problem. If they stay bright and you only get a click, the battery is probably fine and the starter is the suspect.
That second case is one a jump start won't fix. Starter work is a job for a repair shop, because we don't do mechanical repair.
A good battery with a bad connection
Clicking can also come from a battery that is fine but badly connected. A loose clamp or a crust of corrosion chokes the current. With the engine off, try to twist each battery clamp by hand. If one moves, the connection is loose. Don't touch any white or blue-green crust with bare skin.
The cables matter as much as the clamps. A cable can corrode inside its insulation where you can't see it, and a ground strap from the battery to the body that has worked loose acts like any other bad connection.
A slow crank is a warning
If the engine turns over, but slowly, in a long drawn-out rurr-rurr-rurr, the battery is weak but not finished. That is the sound to act on before it turns into clicking. Weeks of slow cranking are the best warning you will get, and replacing a battery on a day you choose beats doing it in a parking lot at night.
If the car clicks and you'd like it running, a jump start is $49–$75, plus the $19 dispatch fee, which covers sending the driver to you. Average arrival is 30 minutes, and the actual time depends on your location and traffic. Tell dispatch what the lights did, so the driver knows whether a jump is likely to work.
Common questions
A few tries are fine. After that, a battery that is barely hanging on gets drained further, and cranking again and again heats the starter. If it hasn't started after several attempts, stop.
A battery near the end of its life can have just enough to start the car on a warm afternoon and not enough on a cold morning. Clicking that comes and goes is often an early warning.
No. A jump start answers that quickly. If the car starts and keeps running, the battery was drained, and the question becomes why. If it keeps clicking even with a jump, the trouble is somewhere else.