A capacitor charging circuit consists of a battery, an uncharged \(20 \mu \mathrm{F}\) capacitor, and a \(4.0 \mathrm{k} \Omega\) resistor. At \(t=0 \mathrm{~s}\), the switch is closed; \(0.15 \mathrm{~s}\) later, the current is \(0.46 \mathrm{~mA}\). What is the battery's emf?