Why does the Battery not stay charged?

If the alternator is good and the battery is new, then something is draining the battery while it's parked. In the old days people left their headlights, radio or something on and this drained the battery. Now a days this is not as big a problem with 5 minute timers that turn off lights if you forget. I would take it back to whomever did the alternator work for an answer. How old is the battery? You can take it to see if it can't hold a charge any longer. In my experience, most batteries don't seem to hold a charge after about two years. Did anyone do some custom work in your car that requires electricity? It could be this extra stuff is draining the battery.

Have you checked alternator output on the car, and will the battery stay up if you disconnect the cables overnight ?

You need an auto electrician to check out your vehicle's electrics.

Check the charging relay if working. You can find it in the fuse box which is either in the engine compartment or under the dashboard on the drivers side legroom.

The 60amp fuse probably is in the circuit between the alternator and the battery. Which would be why the battery is not getting charged.
Someone would need to check for a short in the wiring between the alternator and the battery.

If the battery is new, and you are sure it is ok, either the alternator is not charging the battery or there is something in the car that is using power when the key is off.
You could disconnect the battery at night to see if it stays charged, and-or have the alternator output checked.

The alt should charge at around fourteen volls , any ways, yogi need to put another battery. A weak alt will kill a good bat.and vise versa

check voltage regulator

Check the battery strength and then double check your alternator to make sure it's charging.. I installed 3 alternators, new off the shelf, on one vehicle, and all three were duds (4th one worked fine). If the battery does not need replacing, and the alternator is charging, double check and make sure no components are left on such as a light in the glove box.

1st thing to check would be the alternator, to make sure it's charging the battery. If it's not, the red battery light would come on. Most major parts stores offer free battery and charging system checks, they can tell you if the alternator is not charging. Have it checked asap, as the new battery will be dead soon if it's not being charged. countrycurt0