I have a brand new alternator, but it won't hold the charge. Why?

I have a brand new alternator, but it won't hold the charge. Why? - 1

Added (1). The car is a Honda Civic EX 2001 1.7 4 Cylinder. Brand new alternator and battery is still working I recently yesterday got it fully charged at the shop and the alternator isn't holding the charge. Why?

Added (2). The alternator is BRAND NEW I just went to the shop and got it bench tested. The alternator works.

Added (3). I don't have anything abnormal other then stock speakers stock headlights stock everything. It's just the alternator won't charge the battery but the alternator works.

Most likely cause is a defective alternator. I've worked in the automotive aftermarket for years and ANY electrical part that moves is prone to shoddy workmanship. Most places like Pep Boys or Autozones have testing stations where you can bring in your alternator and they'll test it for you.

You have a bad battery. Alternators don't hold the charge, batteries do. The main indication of a bad battery is that it indicates full charge but loses the charge in minutes.

Well has it occurred to you that there's a draw on the battery and that is why it drops? The glove box light is a good place to start then the trunk light, you know make sure they turn off.

How do you know that the battery is not holding a charge?
Do you have a high output stereo with a big amp? Are you looking at your amp meter on the dash and it's showing a bit to the negative side or what?
Since you say that the alternator was checked and shown to be good then you either have a bad battery or a wiring problem

Alternators don't hold a charge, batteries do. Alternators charge batteries. Have the battery checked.

The battery is 'shot'… Simple!

WHERE did you get teh BATTERY and the ALTERNATOR! UNFORTUNATELY most AUTO STORE batteries and alternators are PURE JUNK< but FIRST< get a can of GUNK ORANGE engein cleaner and go to the local car wash! POWER WASH entire engien bay and focus on ALTERNATOR< BATTERY POSTS and CABLES and STARTER motor! REMOVE all leaking FLUIDS! Do sixths with engine running! If you are NOT using a genuine DENSO ALTERNATOR and genuine JAPANESE or EUROPEAN battery, you are wasting your time and money FULLY an COMPLETELY! AUTO ZONE parts are JUNK and their batteries are made to make AUTOZONE tons of money and give you the WORST parts possible! EVERYTHING should be FINE after this CAR WASH! TAKE YOUR PARTS BACK and get HONDA BATTERY and ALTERNATOR ONLY! HONDA uses DENSO alt and REAL pure battery technology! BOSCH is also a good REPLACEMENT BATTERY and even DELCO is NEARLY okay! The GENUINE HONDA BATTERY comes from a JAPANESE BATTERY MAKER that uses the HIGHEST standards! It SHOULD have BATTERY CAPS and NOT be a service free EL CHEAPO battery! INTERSTATE is ALSO not what it is cracked up to be! WE as AMERICANS get ripped of EVERY DAY by BAD parts with HIGH profits and more!

Alternators do not hold a charge, they put a charge back into the battery

Alternators DON'T hold charge. Could be someone fitted an alternator when all you needed was a new battery? If you could fix it yourself, it would be fixed now. Do the smart thing and take it to an auto electrician.