Just purchase this 2002 and notice that after charging indicates 100% after about 15 minutes of driving the rate went down to 15% (not sure if gauge is reading correct); headlight was working and stopped working, taillight and dash indicator is working okay; general question, should the main disconnect be on or off when charging. Provide resources to purchase parts and accessories
If you don’t already have one, the first thing you need to do is invest in a reasonable quality digital meter. This will help you diagnose odd problems going on with your car.
Being a new car to you, the next thing you should do is determine the true condition of your battery pack. Most of these cars are sold as “fresh batteries just installed” but can be 6 mos old. Depending on conditions submitted by the PO and care some batteries will be wasted by now. It is also possible a cheap set of batteries were just tossed in just to sell the car.
You need to start off by getting to know the details about your car. When you have a problem you would like to submit to the group, you need to list a few more details that may be relevant to your situation. Realize that there are many reasons your car would be acting this way.
The only positive answer I can give you to your above request is - Yes, the main battery disconnect needs to be switched on for your car to charge properly.
This forum has an awesome archive that is the result of thousands of hours that was indirectly built by people way smarter than me just by answering questions and solving problems. When you have a spare moment, explore the use of the magnifying tool in the upper right of your window.
To give you a head start- search “battery dies” and see if other people have had the same issues that describes your situation.
Also look into how to do a Brake Stand Test. This will help figure out your battery pack condition.