Had my alternator rebuilt, but batteries still go dead.checked alternator shows charging at 11.9 volts then jumps to 15 volts after 2 minutes. is this the alternator

amps or volts
11 to 12 amps indicates nothing but if it is volts then it indicates that the alternator is not charging the battery
Battery voltage is 12 -13.5 volts and when charging is 14.5-14.8 volts dc
the rest of your statement indicates that the alternator or voltage regulator is faulty and you should have the charging system checked by an accredited auto electrician

Get a cheap digital voltmeter put it on the DC volts range. Place the red lead on the positive terminal of the battery and the black common lead on the negative terminal. Jump start the car again to get it running. If the battery reads in the range of 13.6 Volts DC volts then the alternator is supplying enough power to charge your battery. The alternator must generate more than 12 volts Direct Current to charge a battery. Also check the belt is not slipping on the alternator pulley.

replace the battery .(has someone in the family/friends got a similar battery you can "borrow"to check before you buy.worth asking???

With engine running used a voltmeter and check voltage at battery, you will be checking alternator out put voltage, should have a reading of no less then 13.0 volts, if less bad alternator, the reason it keeps going dead is that the car is using the battery to run it .till the battery has no more power, then you jump it and the battery is charge up again and will run again till it goes dead again.

Could be couple of things,
A bad battery not holding a charge, should be a little over 12 volts with engine off.
A bad alternator not charging, should put out between 14 to 15 volts with engine running.
If there is an advanced auto near you, take them there, they will check them for free.

Your alternator is faulty.

check to make sure the alternator is charging the battery.crank engine while idling the alternator out put should be 13.5 volts to 14.5 volts. if not alternator is not charging the battery.if alternator is charging battery.the battery is weak.if its over 5 years old its more likely battery.if battery not old checks out good .replace battery cables..

bad generator

if the alternater light is not on the battery.probably has a bad cell

Miserable engineering.

My '95 SL2 purchased new, ate 6 (SIX) alternators, that fantastic "27 patents" automatic transmission, two sets of front disks and finally dropped a rod cap at 56,700 miles of very civilized driving.

I 'sold' it to my youngest son for $1 as a hobby when he got bored with his Jeeps or to donate it to a fund-raising bashing contest.

Now, the reason the alternators die -

They are buried in the engine compartment and get hardly any natural cooling there and, I don't know what kind of stupid engineers GM employs these days, but that alternator at 105 amps rating must deliver up to 1200 watts of 12 volt power an d it is too small to effectively dissipate the 1200 watts of sheer heat it produces while doing it.

If you have any appliance that absorbs 1200 watts (10 amps at 120 VAC), just check to see how much heat that is and even if spread over a larger area and bulk of the alternator, you think that would be a good environment for the semiconductors that are used to make the DC and regulate it.

It's a absolutely insane design and convinced me to never, EVER buy another anything from GM!

Sorry to vent but it still irks me after over 4 years of trouble-free Subaru ownership.
I wish you luck.