At 4.5 AH, you are not talking about a smoke alarm which I assumed [my error when re-reading] from the original post. This must be a multi zone fire/intruder alarm with a lead/acid gel style [whatever they use today] rechargeable and kept under float.
As stated, the only things that matter are the voltage and that it fits. A little extra capacity is all good, reflecting newer technology. If you are happy replacing it OK but you would likely find it would test "good" and last another year if you so desired.
