What could kill the battery while sitting over night

1. are the posts clean
2. is there an extra wire on any post?
3. are the connections tight?
4. how old is the battery?
5. It really appears your battery is worn out
6. how are the liquid cells (distilled water) if neede
7. Let me know how you make out ,
8. Cheers
9. Sir Dana

Your head light switch is the only thing that is capable of turning your head lights on, so I would replace it ! On the other hand you could have a mouse living in the dash, that has chewed through some wiring and at night when it is active it causes a short to turn the lights on. But I would would start with the switch lol

Sounds like something is running your battery down at night. Have you added any new equipment to vehicle? Something is pulling ampage.

you have a short somewhere it kills the battery after sitting all night make sure no lights are staying on for example you glove box light if it doesnt shut all the way light could stay on and you dont even no it.

might be an old alarm system ddraining battery

Have the battery load tested, it may have an internal draw that kills it. Autozone and others do this load test for free.

I just did this repair 2 weeks ago. Hope it is the same for you. It turned out to be the ignition switch. Not the actual tumbler that you insert your key in, but the switch mounted to it from behind. The part is $40. at Autozone. Remove the lower plastic steering column cover. Remove the plastic knee panel. You will see it screwed onto the the key column. It's most always white. It may function properly but inside this little switch are many contact points that when they fail, cause power to draw from your battery. For instance, you'll be able to turn your radio on and run your windows down even after you remove the key.

you can dissconect the electric switch at the latch just pull the carpet away from latch and un plug

Are you sure it is the heater that is draining the battery? If you are sure it is the heater blower that is causing the problem try pulling the heater relay, let it sit over night and check the battery. If it starts then either troubleshoot the heater problem further or leave the relay out...good luck!

HAVE YOUR MECHANIC CHECK THE FUSEABLE LINK BY THE SOLENOID. IF THIS LINK IS BURNED THE ALTERNATOR CAN NOT SEND CURRENT BACK TO THE BATTERY. IF ONLY PARTIALLY BURNED IT MAY SEND CURRENT, BUT NOT FULL CURRENT TO KEEP UP WITH THE DEMANDS THE HEADLIGHTS PLACE ON THE BATTERY.