99 elantra alt not charging battery' installed new alt and battery and fuse good and still no charge on battery

How old is the battery? In general, vehicle batteries are considered 'old' after 5 years especially on bigger engines.
Using a volt meter or a multimeter set to Volts try this. With the engine off and the Keys out test the voltage directly on the battery. You should get a reading somewhere around 12.6 to 13.2 volts. Start the engine and retest the battery voltage. If the alternator is working correctly the reading should rise to somewhere around 13.6 to 14.2 volts.

the alt is what keeps the battery charged. the only way to fix it is to have it rebuilt or get a new one.

Check your battery terminals for corrosion. That will prevent battery from taking proper charge or for that matter supplying enough current to turn over the starter motor.

And make sure that your new alternator is charging properly - when running measure system voltage - should be around 14.3 or environs. If you get reading close to 12 unit is not working!

the best way to test an alternator is with a load test-partstores dont do that--battery may still have a bad cell even tho it tested good--an alternator can burn up charging a completely dead batt--make sure batt reads at 12.6volts and no less-----if it reads say at 12.3 its only 50% charged!

First make sure both battery cables are free of corrosion and ground is secured to chassis and engine then check to see if theres an alt. fuse or bat. fuse blown. Another way to test charging sys w\out an meter is to remove the ground terminal from the bat. with the car running, if the alt. is good car stays running, if all else fails take the alt and bat to a parts store that will test them for free

Battery is only used to start engine.
after charging battery, start car. remove Negative cable, if car dies, wiring to alternator is faulty.

if continues to run, shut off car and all accessories. install ammeter between Neg. cable and battery, if it shows a draw, pull fuses one by one to find circuit with draw while car is off.

Check for a blown fuse, if I remember right Oldsmobile had a charging fuse in those years.

yes if the battery is low it will make the alternator work harder and burn it up

1) check 10A fuse in the batt. juction box (eng. comp.) hot at all times.
2) check the large red battery wire to the alt. for good conn.
3) make sure the alt. is grounded properly
4) gray wire sent from the alt. to the PCM
5) blue wire sent from the PCM to the regulator (alt.)
6) small red wire power frorm the 10A fuse
if all checks out and still not charge replace the alt.

Check the drive belt tension and wiring connection at the alternator and at the battery. Check for a blown fuse in the fuse block . -hope this helps