Hey guys, i have a 2001 7.3, ext cab, 4x4 with 327k on her. on friday feb. 1st it started in the morning fine, went to school parked in the 15 degree weather and 3 hours later i went to start it and killed it when cranking. so i tow it home and jumped it later(about 4 hours after batteries originally died) it started and ran for a hour, i went to dinner shut off. started after dinner again fine drove about 15 minutes home. shut off. try to start 10 minutes later, nothing. completely dead. so saturday morning.. feb. 2 i got 2 new batteries, higher then stock cranking amps. etc. put them in, starts and runs fine all day. sunday feb. 3 morning; window was very slow to go up, didnt think anything of it. drives completly fine, starts fine all day. so sunday night about 8 i left meijer go to start and it took a little longer to start but had strong juice, no problems cranking. drive 15 minutes home. then about 30 minutes later go to leave, cranks really weak. barely started. on my way into town my radio went out, and volts dropped. then eventually came back. so today i go out, starts(very weak) drive 3 minutes to auto zone to get alternator test (new alternator already) shut off. both batteries are dead. jump and starts fine. now i noticed the belt is very loose and chewed up, also squeaking. could this be caused by the alternator not having enough tension to spin fast enough to charge the batteries? all 4 battery terminals were clean with no corrison. so i dont believe they are corrodid deep down in the wire. what should i check next? just tried to start and it doesnt have enough juice to turn over. ( new starter, alt. and batteries) thanks! let me know what to check guys, im falling behind. i got side jobs to finish and no truck to get parts in!