2017 Volvo XC60 Electrical System

The support battery for start/stop started to show on the dash and tells me that service is required about 2 weeks ago. "THE LOCATION OF THE BATTERY IS MY CONCERN". A month ago, the air coming out from the vent of the ac/heater started to smell like a rotten egg, a very strong smell that gives me a headache and makes me dizzy. This smell comes and go.I had to open the windows and switch to recycled air, this helps a little bit. I brought my Volvo to 2 shops about 3 weeks ago before I went to the dealer on Feb 16, 2024. The first shop smelled it and said they checked the catalytic converter and run a diagnostics and emission and they said emission is very good and there is no problem with the catalytic converter and suggested to bring it to the dealer. They said it could be coming from the battery and I told them that the battery is new and main battery has a box casing so the strong smell is definitely not coming from the main battery. I didn't know that there was another battery. I brought it to an exhaust shop and said the same thing, no leaks in the pipe and catalytic converter and smoke coming from the exhaust looks normal and smells normal. Next I brought it to the dealer and they did nothing and simply stated they could not duplicate the problem. I had no choice but to do an extensive research to find out where the location of the support battery so I can change it myself. I always wondered why the smell is so strong in the passenger side intake screen cover of the cowling. I couldn't believe where Volvo had placed the second battery/support battery. It was on the passenger side, right next to the air intake for the AC/heat of the car and is covered by the cowling between the windshield and the engine. Harmful gases that can potentially come out from the battery is directly suck in to the intake of the car's air conditioner.