Is starter working?
If you need to jump start the car then the battery may be fully charged but it is defective and needs replacing. A full charged battery will read 12.6 volts at the posts with the engine not running. 12 volts indicates the battery is only 25% charged.
As long as the battery is fully charged it will start no matter the condition of the alternator. Eventually the battery will run down if the alternator is not keeping it charged.
As long as the battery is charged
if the battery is good and charged sure
Yes.
Yes they could be cleaned and battery charged
Low/bad battery, bad battery connection. If the battery isn't getting fully charged you might not be able to start. If it isn't getting charged, check the alternator.
Check the charging system with a voltmeter to see if it is charging the battery sufficiently A fully charged battery should read approx. 12.8 volts without engine running With engine running should read approx. 13.8-14.2 volts
It will start if there is enough charge in the battery to turn the engine over. However if the alternator is weak then the battery will not be charged fully.
Needing Far more information than that... like did you turn the key? is there gas in the car, is the battery charged, when does it do this, what sounds or symptoms are going on when it doesn't start. Give us something to work with and someone may have a helpful answer
Battery is dead.
You can hook the battery charger to the battery in the trunk, or to the jump start posts under the hood.