If you question the condition of your vehicles battery, drive to your local auto parts store and they can test the battery and the charging system of the vehicle for you at no cost.
Batteries should be replaced about every 3 to 5 years, some can even last seven. However, it is obvious that if the battery dies (with no ability to "jump"), is corroted, or gets a dead cell in it then it should be replaced.
The battery is weak and should be replaced, with a charged one or new one.
While the car is running the alternator should be recharging the battery faster than stereo can drain it. I suspect you either have a problem with the alternator or its time to get your battery replaced. Until you get it fixed, if you don't turn on the radio, it wont drain your battery :) If it is a high power model, it needs to be wired directly to the battery.
It means the battery has been drained of all it's power. Simply recharge the battery with a battery charger and it will be fine. You do not have to replace the battery, although draining the battery fully does harm the battery. Charge the battery fully and it will function as it should.
Although there is no set on how often your brakes should be replaced, I would just pay attention to your car. When you notice something wrong, I would call your auto body shop.
A car battery should not be "cycled" as in fully discharged and then recharged. Such a cycling would quickly destroy this kind of battery. A car battery is discharged slightly when you start your car, then it is recharged again when you drive your car. Proper charging whilst running car engine is good for the battery. A normal car-battery (Lead-acid) can last for many years if not "cycled". Never discharge battery more than 50%. How often you actually need to recharge your battery depends on how it is used.
It should not need to be replaced under normal conditions.
The life of a car battery really depends on many factors, in addition to time. Amount of use and climate are key factors in the life of a battery. One can expect to have to replace a battery generally every 3 or 4 years, however.
Check the battery cables or starter.
im guessing that your talking about the alarm/keyless remote. You will find that you have to get closer and closer to the car to be able to unlock it. You should replace the battery when you have to be within about 10ft from the car.
Yuor battery is leaking fluids or gases. The battery likely needs replaced.
Maybe the car needs gas.