In this one-day lesson, students use their knowledge of fractions to estimate how long it takes phone batteries to charge.  This is a rate problem, and also an opportunity for students to deepen their understanding of fractions and percents, using a context they are familiar with and a visual bar model.  Students use their implicit knowledge of phone battery to estimate how much battery is left using percentages or fractions, and then develop their own strategies to estimate how long the battery will take to charge.