Battery keeps going dead . The Alternater is charging and the engine starts and runs fine for a while then all at once goes dead.

you've had the misfortune of getting a bad rebuilt alternator-sorry-they should give you another one -I hope its not hard to replace-Denny

Does it go dead after sitting for a few hours? Once started and driven for several miles will it restart if the engine is shutoff? If the battery goes dead only after sitting for a while with the engine off, you probably have a bulb or some accessory that is draining the battery.

Check you're alternater, and battery to see if they are working properly

Could be..... the batery is just used for starting, once the engine is running it pulls electric power from the altinator, if the altinator which also charges the batery, is not working power is pulled from the battery, and when the battery goes dead, the car does too. When the Car turns off, do you then need to jump it to start it? if so you could be pretty convinced that the altinator is the issue

First tell me why you don't think it's charging.
Because of the voltage reading you are getting at the battery terminals? The range you want is between 13.6v to 14.2v. The higher the voltage the lower the amps. and true the other way, the lower the voltage the higher the amps. If you get a reading of 13.6v or lower, the alt is nearing or at max output. An alt can only run at maximum for around fifteen minutes and it will start slinging solder from overheating. It's a good indication the battery is either totally dead or junk. Charging above 14.2 the alternater is running wide open and is only putting out high volts which will cause the battery to boil , in turn destroying it. This is a bad alternater. All alternaters have integrated voltage regulater with the exception of ver few of the earlier ones. You cannot test an alternater by removing a battery cable to see if the engine keeps running without taking great risk of damaging the alt, regulator. So tell me why you feel it isn't charging. Remember an alt is not made to charge dead batteries. Their sole function is to maintain the battery charge. Without a battery, the alt won't last 10 seconds.
Hope to hear from you and good luck.

keep in mind, your engine use both source of power to run, one from the battery and one form alternator. If the alternator is good, your engine should stay running regardless if the battery is good or bad, the alternator should keep the engine running. It sound like to me the alternator is faulty not charging your battery or keeping your engine running, even though the alternator is brand new does not mean is good. My guess I would take the alternator back and get another one. the reason why your car ran for 25 min and die it has no source of power to keep the sparks going although the alternator should keep the engine running and at the same time charging the battery but is not.

u may have parasitic load what that is when like somethin on the car stays on even if u shut everything off causing to drain the battery

ALTERNATOR NOT CHARGING

start engine and hold rpm about 1500 turn all light on and wipers heated rear windows the lot ,if engine stops the altenator is U/S if it all keeps working and engine running change the battery

Does the fuel pump stay running at all like when you shut off the engine?