WHY WON’T MY CAR START?
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. But if the alternator or another part of the electrical system in your car is damaged, the battery will not recharge and neither a mechanic nor a service station will 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.