losing battery voltage in new battery

I purchased a new battery in February 2016 thinking that this would solve the problem. The battery gauge has a normal reading when I get in the car. From time to time the battery gauge will drop below normal and just before that happens I begin to smell roasting peanuts, I know, it sounds crazy, but it is happening. This does NOT happen daily or on every drive. So when I went for routine maintenance, November 20, 2016, I mentioned this to my mechanic. He checked the battery and the alternator and the battery was reading low. Alternator and wiring harness in good condition. So we changed the battery again- of course it is covered since it is only a few months old. So on November 24, 2016 my car was rear ended. It sat in my driveway until December 1 when I took it to the body shop. I got it back Wednesday, December 14, 2016. So yesterday, I am driving home from work and I noticed the smell, and within 5 minutes my battery gauge drops below normal. Everything I have read states it is an electrical wiring problem, but I do not see how there is no problem with the wiring harness from my battery to my alternator, but the battery is being drained. Is the battery causing the smell? The battery in this car is located under the passenger seat, so I can assume that I would smell a battery problem inside the vehicle..... I need help. Not sure what is going on, but this needs to be remedied.