So on Friday, after coming from office when I shut off my H3 (06):
- Parking gear indicator light stayed on.
- When I removed the key, light stayed on.
- When opened the door, chime started as I left my keys in.
- Today (Saturday) morning, battery died.

I googled a lot but everything is re-directing me to ignition switch replacement.

So question to all gurus, what is the reason behind this?

As always thank a lot in advance.

Here is the pic for the same.

 

It would appear to me that you have a short in your ignition switch..... it still thinks the key is in and turned to the Accessory (ACC B) position. Not unusual given the age of your vehicle, especially if it is a daily driver... the key gets turned on and off a lot.

A new ignition switch is not a high ticket item and can be a DIY.

 

Looks like you have an aftermarket alarm by the key fob.

May also be an issue with that.

 

I did LoJack and Alarm system installs for 12 years. Again if the ignition switch is worn and not releasing and going to full off the BCM ( Body Control Module a computer controlled relay pack that says keys in and on I need 12 volts to the radio,power windows, dash lights etc etc or keys off I will shut all power down in about 5 minutes or after I see the key removed and the door open ) will since power and turn on a few things and leave them on therefore draining the battery. If you have an aftermarket alarm tied into the illuminated entry you may have a relay stuck on the alarm board and its telling the BCM to stay on.
Your aftermarket alarm should have 2 fuses tucked up under the dash. Pull them and see if the lights go off. If not I would say put the key in and cycle it back and forth a few times remove it open the door and see to see if the power shuts off.
I too lean toward worn ignition switch.