Can a 3 year old battery go bad? Sure.
Is it the kind that has caps or plugs that can be opened to see the battery fluid level? Check and fill to line with distilled water.
Jump start. Remove jumpers. Seem to rev ok?
While running, have someone sit in the car and rev to 2k and measure the voltage across the battery posts. ~14.4V? OK, alternator seems to be working.
Drive OK? Drive for 15+ miles with a/c off and in daylight. Should now be charged.
Stop. Measure voltage. at least 12.5+V? OK.
Or drive to a battery place and get them to test the battery.
Does completely draining the battery hurt the battery life? Yes. One time fatal? Usually no.
Any aftermarket add ons that are in the car that could be draining the battery? Electronics, alarms, radar, phones, etc?
The trunk lights go off after about a half hour on mine. Been there, done that. Battery wasn't drained when I came out and saw mine the next day with the trunk (or door) still open.
I'd not just go swapping the battery before understanding what is draining it.
There is also a way of removing a fuse at a time and measuring the current drain to see what circuit the drain is coming from.
And if you do replace the battery, there is no need to pay $200 when there is a
whole list of perfect fit ones.