That one is a bi___ to find!!
Committed to changing lives.
www.phonak.com
This will get you to their site, then download the user manual. If you have one of the models they show, it tells you the battery size--you can then search for hearing aid batteries of that size--it SHOULD work.
Or call them and ask for customer support to give you a better number. (IP532328 does not return any usable results on google, that I could find)