my girl friend just bought an early 99 f250, 150,000 miles with a hand shaker....good price....the truck was sitting for a few months and our friend needed to unload it...he charged the batteries and dropped it off to her house...we bombed around the block a couple times untill she got it registered. ran great with no starting issues...hopped into the truck on friday and it wouldnt crank over fast enough to start up...so i hooked up the charger to the passenger battery just to give it a little help to crank over. got it going and drove it home. left it running for a bit....drove it a little saturday evening all was good, sunday morning it was good untill the ride home....i noticed the lights were dimming...the radio lights were flashing, and the windows wouldnt work. i figured the alternator wasnt charging and needed to be replaced...i got home from work today and tried to close the windows and when i opened the door i noticed the dome light was very bright. i thought that was strange...turned the key to the on posistion and noticed the voltage went from like 12 volts to like 9 in a split second...the windows wouldnt go up with the key in the on posistion but when turned back into the off posistion they went up. do i just have a bad battery on my hands or is it something else? i just thought it was wierd to have 12-13 volts and then it just drop wicked quick...maybe its because of the load of the glow plugs??? any input is appreciated.