When it rains my cars battery dies, i have no idea what happens because it's usually after two days of steady rain. do i need a new battery? or alternator?

Test the battery first...
Clean the cables, battery ground "body" connection, terminal ends both ends of ground from engine to body and all wires that attach to starter.

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If it only goes dead after it rains, I would take a look around for a bare wire that may be shorting out when it gets wet.

ok thanks, i'll check it out tomorrow morning