NEW BATTERY, REPLACED ALLTERNATOR, WHAT VOLT METER SHOULD READ, THE CAR STILL DRAINS THE BATTERY, WHAT CAN I DO?

The car needs at least 12 volts to start up, after that it usually jumps around from 9.3 to 13.5. Is the alternator new or used?

a charged battery is 12.6 volts, not 12, it should be putting out 13+ (at least!)when running to charge the battery sounds like you have something putting a drain on your battery, which can be quite hard to find, most common causes are aftermarket stereo gear, alarms etc etc your best way to source the issue is to use an ammeter to check for current draw at the fuse block when the car is off. just pull the fuse out and put the ammeter in its place it should show weather or not theirs a draw in the circuit

Catera's are unfortunately one of the vehicles known to be notorious for electrical problems, among other things. Is there anything in the car that is malfunctioning or not operating properly....from gauges to power controls....odd noises... It's possible you've got a relay hanging up and supplying power to a circuit that should be dead. Pull the key out, shut and lock the doors and wait for everything to time-out... Any noises? Any lights staying on? Go K.I.S.S. on this one and start simple.... The most overlooked culprit of draws, aside from aftermarket stereo equipment, are overlooked interior lights such as kick-panel lights, dome lights on the wrong setting, etc.

what amps are needed on a 99 Cadillac Catera battery?