Renaureal

Hey guys! I was reading Deception Point by Dan Brown where he mentioned that his explorers were able to recharge the batteries of their microbot simply by placing it "near the cylinder of an electric generator". I was wondering whether recharging would actually be possible without direct connection to the generator. Would that be an effect of the 'leaking' magnetic field? Still, how can only exposure to a magnetic field raise the potential of charges stored in the batteries? That made me confused and any help would be most appreciated