need help quick plz

ok my friends car its a 95 dodge intrepid and he went to start it and it just clicked like the starter was bad b/c all his lights worked and horn but ive seen cars do that and all it need was a jump so we jumped it it started and ran fine but then we looked in the batt and nothing was in it no acid so my ?? is what causes this

could really ues help thanks


JERRY

1974 duster (in progress)