Will the Citrus Fruit Battery With the Most pH Create the Most Electricity?

Science Fair Project Information
Subject: Electricity
Grade level: Elementay School - Grades 4-6
Academic Level: Ordinary
Project Type: Experimental
Cost: Low
Awards: 2nd palce, Selah Intermediate School (2002)
Affiliation: Selah Intermediate School
Description: The pH of different grapefruit, orange, lime and lemon fruits is measured by a pH meter. Build home made batteries by sticking a nail and a copper coin into fruit halves. Then use a voltmeter to measure the voltage.
Links: http://www.selah.k12.wa.us/SOAR/SciProj2004/SamanthaH.html