By creating a hypoxic environment, the battery significantly boosts the efficiency of HAP cancer medications (hypoxia-activated pro-drugs) that seek to exploit this trait by only killing hypoxic cells. Previously, no HAPs have been approved for clinical use due to limited evidence of their effectiveness. "After 14 days, the Tumors in the five mice that received both the working battery and HAP treatment had decreased by an average of 90 percent," said lead author Professor Fan Zhang, of Fudan University in Shanghai, China, "with four of these mice experiencing complete tumor disappearance."