After my hatchback has been open for more than 15 mins, it kills my new battery too.
This is most likely because when the hatch is open the cargo lights stay on. I'm not sure about your specific car but in many cars you can deactivate the cargo light with a switch in the rear of the vehicle. 15 minutes is a short amount of time for a battery to die but I would need to know more about the battery and car to give a response to why the battery is being drained so quickly.
@inthedetails
about the car, it's a 2014 Honda pilot touring, 190,000 km, I checked for lights and all lights are turn off.
I thought maybe, the battery going dead so fast was because the battery was pooched so I bought a new one for it, but the condition stayed the same. Does it take power, (lots of power) to hold the hatchback up and open? The hatchback works perfectly, other than the draining the battery thing. When I use the hatchback, I make sure or try to keep it open no more than 5 mins. It seems my wife can't remember this rule, and sometimes I too at times get distracted and find myself in an embarrassing situation. Oh yeah, I live in Sudbury, Ontario, Canada and it's not uncommon for the temperature to hit -35 F. below and I park outside and never plug in my car. Oh yeah I even checked at night to see if any dome light stays on, but never saw any. I've left the light on, in other vehicles and the snow was melted on the top of the car over the light in the morning, but I never see this with this car. What else can I tell you?