More info will be needed to properly answer your question.
There could be a multitude of reasons.
Does your vehicle start at all? Does it stall while driving or idling?
Insert the ignition key into the ignition and turn it to on, the alarm should shut off.
Internal short in the lead plates, time for a new battery.
Since it is not urgent that you get a new car battery, I would suggest looking on Amazon or eBay. I would also look at your local junk yard.
I've never tried that, but I am pretty sure the battery would no longer work.
Car battery coupons usually last about 2 months. Once you find a coupon, I would buy a new batter.
A short somewhere along your electrical system. Or a faulty battery. Next time you come in from a drive, disconnect your battery from the car, leave it off for greater than 5 hours. Then re-connect your battery after 5hrs time and see if the car will start. If the car starts then your battery is OK and you will have to trace the short in your electrical system. If the car doesn't start then buy a new battery and you're good to go.
When buying a car battery it is best to choose one with an extended warranty so that if anything should go wrong with the battery or it isn't charging correctly, the company will replace it at no charge to you. I would buy a new car battery with a warranty instead recharging your old one.
You can get a new battery, you can jump start the car with jumper cables and another car with a charged battery. You can also put a battery charger on your battery to give it a charge.
The the alternator is defective.
Go get a new battery using another car. Or get the dead car jump started using another vehicle. There are companies that have mobile battery services that will come right to your home or wherever the car is located and replace the battery.
I would not buy any battery over 6 months old.
If your battery is dead then you are going nowhere therefore why would you need to take the car out of park? Get a jump start from another car with a good battery and then you can start your car and drive to the nearest battery dealer and buy a new battery if need be. Otherwise just put a battery charger on your battery and let it fully charge.