I've replaced the alt and battery in my truck the battery will not hold a charge,...

[Mark]

...when jumped it will start ? After jump starting it will be fine for the day but if it sits for 6 or 8 hours it won't start.

[ShaneA]

It would help if you were to mention what make model and year your truck is. Sounds like you have something draining the battery, or it is possible that you got a bad battery. Disconnect your battery overnight and see if you still have a problem in the morning. If so, then you have a defective battery.

[stephanieU]

ok got to check your terminals on battery if there s a built up on corrosion.the cable it self can be the source like the positive and even the negative.if so replace the corroded wire or cut the,or both wires about an inch to inch and a half and replace the terminals.if you going to do it ask someone like from auto zone what terminals and how to do it.who knows it might be your throttle valve that needs cleaning ,that ll keep the fuel and air mixture to flow right and your car hard to start and you ll drain the battery.but i m thinking it could be your terminals corrosion and the cables.if so take your car to a mechanic and tell them to cut and replace the terminals if you cant to the job or ask a friend to help you on it.

[MooCowMan]

Especially if it's a Duralast battery from Autozone, test the battery first. It's nto uncommon for batteries to be defective right off teh shelf. Take it to an auto shop so they can do a load test, not the parts shop where you bought the battery BC their testers often show false negatives.

OTHERWISE...

Parasitic draw. Every car draws a small amount of current to keep memory in the stereo, run the security system, etc. Normal draw is up to 50 milliamps (.05 amps). Somtimes something goes wrong and creates greater draw.

If you have an ammeter, you can test the parasitic draw. If the draw is bad enough, even without an ammeter, you can test it. Disconnect the negative cable and barely touch it to the negative terminal. If you see or hear any amount of spark, something is drawing too much current.

With an ammeter: You need an ammeter that can test up to 20A DC. Smaller meters will blow their fuse or burn out if it turns out the draw is greater. Disconnect the negative cable. Connect the red lead of teh ammeter to the negative cable, connect black lead to the negative battery terminal. The ammeter will now show how much parasitic draw you have. If it's over 50 milliamps (.05A), something is draining the battery. With the ammeter still connected, start unplugging fuses to see if the draw drops. Start with what's most suspect, like aftermarket stereo or security equipment, then radio fuse, etc.

It's time consuming, but it can be done.

[bandit_60]

are the battery terminals clean and tight? is the belt tight? it also could be a short in the starter too. it can draw the juice from the battery. i saw that happen before.

[jgood_50]

I bought a car with the same problem. Replaced the ignition switch and it solved it. Drove the car for years.
Also make sure there is a engine to chassis ground wire. If this is missing? It will cause this problem.

[Mosche]

How things were going before changing alternator and battery? If you changed them because the former ones were bad then it really might have some parasitic flow that drains battery while car is shut down. I suppose then that the old alternator and battery were damaged for the same reason. So, you may expect that soon you'll have to change alternator and battery again. Better find the problem...damaged isolation for example.

[chrisw]

u say it wont start. there could be other reasons for this other that lack of battery juice. at what point in the cars history did this become a problem? did it gradually get worse or started in one hit? ur not leaving the lights on by anychance?