renault trafic 02 stop and battery lights flashing intermittently?

hi can someone help me i have an 02 trafic the battery light and stop light are coming on intermitently more so when i first start the van and there is a kind of hissing noise which accompanys the lights flashing it has only just happened after some heavy rain i dont know if this was a co- incedence or has something to do with it since this has started happening seem to have lost some power at the pedals can someone please help