Yes
If the ignition is left in the on position, yes.
Radio Use when engine is not runningYes, use of the radio when the engine is not running will drain the battery. Also, IF the use of the radio requires the ignition switch to be in the ON position, then any other devices [such as on-board computers, electric fuel pumps, etc.] that are turned on when the key is on will also add drain to the battery.IF your vehicle ignition switch has an "accessory" position [usually one "click" counterclockwise from the OFF position, then only the accessories that you turn on, will drain the battery.
yes
In a modern car there are a few things that are still "on" even when the ignition is off, there's a clock in there somewhere, you've probably got an alarm as well ASO. It isn't much, but enough to drain a battery if left long enough, particularly if the battery isn't 100% to begin with.
The key being in the "on" position itself. As for rapid battery drain, you could have a bad battery or there could be a loose connector. Source: Personal experience
No, not unless the ignition is turned on.
Yes, IF the ignition SWITCH was left ON. I suggest charging the battery, and then have it tested at Autozone both of which are free.
It could be a bad battery.
"As long as you put the key in the off position, the battery will be fine. I have had a few lawn mowers with a key start and have left the key in them with no problems." This is an inaccuracy - From 2006 on there is a sensor on the igitions which will trickle drain the batteries as it complets a magnetic circuit when the ignition is off.
Pull battery and let it sit over night. Leave the key in the ignition in the on position to drain whats left of the charge. When you connect the battery back the next day it should be gone. Don't leave the key on when you reconnect the battery.
mainly leaving your lights on when the engine is of or leaving the keys in the ignition
Yes. Otherwise you will drain the battery through the ignition points, burning them out prematurely or even welding them together.