New 320 amp alt over chargeing battery

Yo im new here, building a 2002 f 150  4.2 in to a spl bass truck with blowthrough cutting out the entire back going big 4th order so i bought a new alt its a irragi 320 amp had three wires coming out of it on its harness and my harness in truck had two wires i hooked it up with a buddy left one wire un hooked seemed to run fine tested out at 14.7 i think but soon old battery that had been sitting for a year and was 9 years old lol after chargeing died in truck by next day. Figured it would so i went and got a optmia yellow top battery as a upgrade and hooked er up drove down the  road and back poped hood and the batterys hissing at me trying to figure out the cause and fix and also hopeing batterys ok heard if they  hiss there damaged ill also note we previously removed entire heat air system inside and under hood re routed the heater core hose n stuff useing ac as a pully even tho there disconnected and i think egr may be disconected to just useing as a pully if that may have somthing to do with it neway please help if possible its my a to b ride been buming my gfs lil car till i get it figured out an she aint happy