The external battery [pushes electrons into/pulls electrons out of] the electrode connected to its negative terminal, charging that electrode [positively/negatively]. This forces lead [ions/atoms] of formula Pb2+, to accept two each, changing them into lead [ions/atoms] of formula Pb. This is called [oxidation/reduction], since it involves the acceptance of electrons. Grey lead metal is formed through this reduction reaction. The electrode at which reduction happens is called the cathode. Therefore in an electrolytic cell, such as this one, the [positively/negatively] charged electrode is the cathode.