Putting the lights on, listening to the radio or anything else that is plugged into the car.
Either a short to power or a bad fan switch.
Battery has a dead cell, need to replace battery
Could be a faulty thermostat switch in the radiator !!
Your battery is going bad and something may be draining the battery. If you have a weak battery, it will lose charge. The car charges your battery when you run it and if you dont run it, it will go dead. If your car dies while running, in that case you might need a new alternator.
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.
Can be any light in the car as in, under hood, trunk, glove box, etc. Can also be a relay that is stuck. Can also be the battery has a dead cell and is running itself down.
Something is on draining your battery overnight. Any light or any relay. It can also be your battery has a dead cell draining it overnight.
you can avoid draining the good battery
you possibly have something draining the battery when the car is shut off, with the car shut off pull the positive cable off the battery and then just touch the cable to the positive post of the battery and see if you get a spark, if you get a spark you have something electrical draining the battery.
A battery is used to start a car. Once it is running, the alternator then supplies electrical energy to charge the battery as well as power the electrical systems in the car. Removing the battery while the car is running will not affect the running of the car.
If the parking lights are on when the car is off its probably a switch issue.
many things can do it suck as junk battery, junk alternator , or leaving anything on in the car