Expert auto mechanics: Auto car starter draining battery? Should I pull it out before replacing battery?

Uncle has '05 Equinox with low miles. Since 2005, if the interior lights are left on for 20 minutes, or the hazard lights used for 20 minutes, the battery drains. It's time to replace the battery, but shouldn't I get that starter taken out? I'm his POA, and take him to medical appointments. I don't want to get "stuck" somewhere with him and a dead battery. I'm sure the battery alone will be pricey, but what might removing that starter cost? Also, once when someone jumped it with a portable starter, immediately after I noticed "CD changer error" come across the radio display, and when I open the front door, it makes noises like it is trying to eject a CD. There's never been a CD inserted into that player. Is that a matter of resetting the car's computer? If I don't run the car at least once a week, the battery goes dead, also. This car is in excellent shape with only 22k miles on it, and probably will be sold by the end of Summer, so I hate to get into expensive repairs, but it needs to be dependable when I take him to appointments. I know what every GM dealer will tell me if I take it in, so just wanted an opinion first.