The　current　and　potential　distributions　on　the　large-sized　flat　positive　plate　of　lead-acid　batteries　in　its　formation　have　been　studied　by　an　in　situ　electrochemical　scan　technique.　The　formation　can　be　divided　into　three　stages.　The　first　is　before　15%　charge　amount　At　this　stage,　the　conductivity　of　the　positive　paste　is　dominant.　At　the　second　stage,　from　about　15　to　62%　charge,　the　formation　rate　depends　on　both　the　electrochemical　reactions　and　ohmic　polarization.　At　the　final　stage,　the　electrochemical　reactions　are　a　rate-limiting　step.　At　the　beginning　of　the　formation,　the　distributions　of　the　potential,　current　and　polarization　resistance　are　uneven,　depending　on　the　evolution　of　the　conductive　PbO2　zones.　In　comparison　with　the　tubular　positive　plate,　the　distributions　of　potential　and　current　are　more　uniform　in　the　formation　of　the　flat　positive　plate　and　the　polarization　is　much　smaller.　The　violent　oxygen　bubble　evolution　at　the　beginning　will　result　in　high　contact　resistance　of　local　active　mass.　©　2005　The　Electrochemical　Society.　All　rights　reserved.