key remote not working

[stackz]

ok, so about 2 weeks ago the key remote on my normal use key (backup key has been dead since I bought the vehicle) stopped working. well, every now and then if I just press the key and keep it pressed while standing next to the vehicle, it will unlock or lock. I was thinking the battery finally wore out in it. it is an 01 x5 after all. battery is like 16 years old as this point.

I looked at videos on youtube about battery replacement and so I took backup remote since I knew its battery was dead and cut it open and replaced it with a brand new non-rechargable battery (there's several videos where people do this actually). I can still manually lock/unlock the vechicle and start it with this key but even with the new battery in it, the remote features dont work.

is it because this one has been dead for so long that the chip wont transpond or should I just buy a new oem battery for it. I will say that I dont have it sautered in place, just sitting in the electronic portion of the key. but I even had this section just sitting in my hand and using one hand to press it together for good contact while using the other one to press the buttons, got nothing.

I hear people talking about some sort of radio antenna in the cars that will go bad and stop the remotes from working but...if this went bad, wouldnt the radio itself have bad reception?

just trying to get this sorted out before we have our first child next month as it will be a pain in the ass to manually lock/unlock the vehicle in july heat with a baby in a carseat lol.