Now what you should do is write the radio PIN # in the handbook, if it has one.
I had to replace mine in an old car I bought second-hand, when the car battery died suddenly. When a new battery was fitted, the radio required the PIN be entered within 5 tries. No chance.
Also, the car alarm becomes switched on at battery installation, and can only be silenced with the remote, so you must have that with you, too.
The car is nothing exotic, just a Camry.
And yes, I had to buy an adaptor connection for the job, as Joe says.