Two cells of emf ε and internal resistance r each are connected in parallel. The equivalent emf and internal resistance are

1. For identical cells in parallel, the terminal potential difference stays ε. 2. So the equivalent emf remains ε (parallel identical cells do not add emf). 3. Two internal resistances r in parallel combine as r/2. 4. Hence equivalent single cell has emf ε and internal resistance r/2. _Source: syllabus Physics, Ch 3 "Current Electricity", §3 combination of cells_