Alternator output w/ engine running should be around 14.8 volts. Watching the voltmeter, turn on each load separately, and note voltage drop. Lights and wipers should be biggest draw. Better to do with ammeter, but go with what you got. If one is substantially higher than others, your problem is in that circuit. Then it's a matter of tracking down short, bad ground, etc. Make sure all battery cables are clean and tight at each end.

Bad alternator and or battery

either that voltage regulator inside alternator (IC REGULATOR) is no good or you have serious ground issues somewhere.

Anything above 13.5 volts or so is charging a little with 14.2 to 14.8 being optimum.

Ohms law; it takes a volt to push an amp across an ohms resistance. in other words if charging voltage isn't greater than battery voltage it won't charge. voltage must exceed substantially to charge substantially.

Just because a battery reads 12 volts with no load, it doesn't mean it's any good. If it hasn't got enough power to run your radio, it's had it. How old is it? Assuming your starter motor draws about 200 amps,a good fully charged battery should hold at around 9 volts under a load.

replace it

Alternator is brand new, battery tested good, yet my battery isnt charging, I have voltage reader built in my car so i can tell how much voltage goes thru my car it jumps between 9.5 to 14.1 its good between 12.6 and 13.0 when nothings on accept radio but when i turn on my radio lights windshield wiper and blinkers voltage drops big time what do i do how do i fix it and how much will it cost to fix it btw its a 96 sentra