When you ask yourself, “Why won’t my car start,” you usually refer to the battery as being "dead," even though that's not technically correct. A battery that's merely discharged from leaving your headlights on or from a damaged alternator can be recharged to its full capacity. But a battery that's at the end of its service life can't be recharged enough to restore it to a useful power level. Then it truly is dead, and must be replaced.
If the battery is discharged and not dead, you can jump-start it from another fully charged battery. About 30 minutes of driving should allow the alternator to fully charge the battery. But if the alternator or another part of the electrical system in your car is damaged, the battery will not recharge and a mechanic or service station also will not be able to recharge it. So if your battery keeps discharging, have your electrical system checked before you replace it. What looks like a bad battery could be an electrical system problem. If you have a bad component in the electrical system, it will keep draining a new battery, and you'll be stranded again and again.