for the third time now ive gone out to my truck after school and the battery wasnt compleatly dead, but it wouldnt turn the motor, put jumpers on it for 10seconds and it starts fine. i tested it in auto today and it was charged, it seems to only do it after it sits for awhile and only during the day. i think the hotter weather is finally killing my battery, i also tested the alt and it is working fine, no parasitic draws either

 

well i went and picked up a used battery for $25, hope it fixes it

 

Sounds like a light is on, check underhood or glove box light, happened to me and drove me nuts till I found it was a light.

 

ive checked for lights already, nothing is staying on, went and got the used battery, have to see if it fixes it

 

If battery doesnt fix it, check ALT again. Check Diode in Alt? A bad diode will drain battery when vehicle sits for some time. Bad thing is Alt will charge fine and vehicle will drive fine, and start with no problem on short down time.

 

....used battery? Why not spend the little extra money to get a brand new one? It'll more then likely last longer and then you'll know for sure it isn't your battery.

 

I've had a bad alternator before and it tested good at Advance Auto Parts. If you have a bad cell in your battery, then 9 times out of 10, it'll test good on a computer. I've had it happen many of times on a machine at Advance Auto.

 

A battery with a bad cell will barely start, but not without a jump, battery will die overnight. Check voltage, if 12v batt ok, if 10 or 11 bad battery. Also check when running, you should get 13.8 v this will tell if alt good.

 

since i put the "used" battery in its been just fine, the battery is only about a year old according to the lable on it, and for $25 it was a deal, before hand i did exactly what you said to do and the alt checked out fine

 

Dec 2011 First got the airbag light and code 5-2. Then my batt would drain and die overnight. Installed new battery -- same thing. Then the weird stuff started: dome light wouldn't turn off; headlights wouldn't turn off; engine surging or no acceleration; chirping sounds from inside dash; speedometer dropping to zero -- and none of these things were consistent. They occurred randomly. Only thing that was persistent was the airbag light and code.

In Jan 2012 did the AutoZone checks - came up normal. Took it to 2 different garages - they said $75/hr to run down the obvious "short to ground" problem (and that could be hours to days to do!!!).

In Feb I read on here about the windshield leaking problem that Ford refused to do a recall over. I took it to a window and glass place that mainly does auto window repair. Sure enough - my windshield showed definite signs of leaking once they had it off. They cleaned and resealed within a couple hours. ($85).

******** ALL ELECTRICAL AND ENGINE PROBLEMS DISAPPEARED !!!!!!!!!!!!!!

246 Starter cycles later the AIRBAG LIGHT AND CODE WENT OUT!!!!!!!!!!!!!!!

So for $85 my 98 f150 runs perfect after 2+ months of frustration. And I saved hundreds of dollars from having a mechanic run down an electrical short that never existed! It was all due to moisture from a leaky windshield!