mazda323F GXi 1.5 y regn - buying second hand mazda - suziesue

my son is considering buying a second hand mazda it has done 39000 miles - looks in good condition - when would the cam belt need to be replaced. It has electric windows - sun roof A/C etc. But the battery was run down the guy in garage wasn't sure why - checked the battery not the original - could there be a problem with the electrics??? Any advice please pref ASAP as he needs to make a decision. PS the price is £1500.

thanks