PRAM Battery MacBook Pro Core Duo 15 Inch

Hi

I have had my Mac for 4 years and no problems with the PRAM battery. I am planning to replace the hard drive soon and considering replacing the PRAM battery at the same time.

1: Do you know the life of a PRAM battery i.e. is it a good idea to replace it even though it appears to have no problems (bearing in mind the battery's age)?

2: Your replacement PRAM batteries are marked 'Used' on the web site with a six month warranty. What total life can I expect from one purchased from ifixit?

Kind regards

Richard