Volts lights comes one; changed battery 3 days

All I can tell you is that when the regulators in the PCM mess up, the alternator usually will not charge at all.

I do not know what you mean by "all over the place", but I can also tell you that if your charging system voltage is really erratic, like 12 volts one minute and nearly 15 volts the next, it is usually caused by a shorted (oe sulfated) battery cell. A shorted cell will cause the alternator to "full field" and make the whining noise you are describing. Also, shorted battery cells are what usually causes the early death of many alternators.

The battery light comes on when there is an issue with the charging system. Most likley you have a bad alternator. With the engine running you should see a min. of 13.5 volts at the battery and better yet 14+ volts. If you have 12.5 or less than the alternator is not charging.

Once the vehicle is started the battery is no longer in play. The alternator is what keeps the power supply to the vehicle and recharges the battery for the next time you want to start the vehicle. Once battery voltage drops below 9 volts or so systems start to shut down. Eventually the battery will drain enough that the engine management system can no longer function and the vehicle will stall.

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with the battery fully charged, you need to check the alternator, but first make sure all of the battery connections are clean , and tight,, with a multimeter, set the meter to DC volts,, place the red lead on the positive battery post, and the black one on the negative post, with the car running, you should get a reading of no less than 13.5 volts, if not you have a bad alternator,, if the reading you get is between the 13.5 and 14.5 volts your alt is fine, and you have something else draining your battery ., but keep in mind that if the cables were in bad shape , the alternator couldn't supply the power back to the battery with the loss it had while starting the car , here is a good link to see how to check the cars electrical system
http://www.aa1car.com/library/tselec.htm

check for 12 volts at the battery if it is anything less you will need a new battery.

sounds like an alternator not charging. You should have 12 1/2 volts with engine off and 14 1/2 volts with engine running if alternator is working.

Hello your battery light is an indication battery is not being charge cause your alternator , will cause the battery light check the belt is it is on and good boost and use a volt meter you should have 12.7 volts up to 13.79 if lower witch i strongly suspect you will need to change alternator and your battery all you can do is charge it and see if it will hold a charge when a alternator does what yours did it usually finishes the battery.Your check engine light you will need to have a OBD2 Scan completed to retrieve the engine fault to properly repair most garages charge $25.00 and up.

the battery needs more power,, it needs to be over 12 volt..to startpay attention to the sound..
you may also not have enough fuel pressure.. you need to tested and must have 45psi
if not you have to replace the fuel pump

Hi there, I am a girl (i.e. not car savvy), but I have a 1998 Altima as well, and the first time (4 months ago) I noticed the brake and battery lights on simultaneously, I took it to a Nissan service shop. Everything seemed fine until about a month ago when the symptoms returned. I ignored the problem for 3 days and the car just stopped running, period. Took it back to the shop, figured out it was a fauly alternator, got it sorted, no problem. Today (1 month after replacement), I see the same bloody problem, and I'm taking it back to the shop in the morning. I am wondering... is it the alternator, or something connected to the alternator that is malfunctioning? The 2 alternators put in were "rebuilt" since they didn't have genuine Nissan alternators available. I really hope the dealers aren't taking me for a merry ride.

If it has worked recently and quit, you may have burned out windings and need a new starter. One way to check is have someone turn the key while you tap on the starter with a wrench or hammer. Strike the case of the starter pretty good. If the starter takes off, this is the problem. It may work a day or two after it gets going again but it WILL go completely out soon.

My 2004 Sebring did just that. it was a fusible link. a tiny square box in there with the fuses. they are a cube that plugs in about 3/8" of an inch square. Find the bad one replace it and the starter starts working again.