1999 GMC Jimmy battery keeps going dead

I have a gmc jimmy 1999 every other day I am having to get a jump because it won't start, it lets me roll down the windows and set the security system but not turn over, I quit using the security system and was using my key to enter the truck and it seemed like maybe 2 weeks before I needed a jump. But not using the security and had to get jumped yesterday and today. Also when I get jumped and it starts it releases my back hatch, hence is why I am wondering about the security system being involved or just bad battery, it is about 5 years old