I was unable to start my Nissan the other day my husband put a new battery in it and tested the voltage it was 11 so he thought maybe it was the alternator he put a new alternator in it then tested the battery voltage it still reads at 11 he has checked all the fuses they all ok as well.He even disconnected the neg battery cable while the car was running the car did not die.I had no lights warning lights come on befor hand to tell me anything was wrong with the car.( we checked all dash lights as well).So what could it be why is the battery only putting out 11 volts when it should be 14?
I assume it was the original 2002 battery. If so it needed replacing anyway.
At rest the battery should be a little over 12V when fully charged. Has it been fully charged? It should be 14+ with the engine running when it is fully charged. If the battery has not had time to fully charge (new batteries are not fully charged) then I would suggest fully charging the battery.
Try removing both ends of the battery cables (both of them) and cleaning both the cable and where it goes very well and reattaching making sure they are secure.
Note: removing a battery cable with the engine running is usually a very poor idea with a modern car. All those electronic things and computers don't like that and it can cause considerable damage.Yes its has been fully charged he even took it out to fully charge it the battery is Brand new .Yes my husband knew new cars dont like to have the cables pulled off the battery he just did the negitve side once.We are at our wits end everything has been checked fuses,belts.
Take a look at the fuse list in your owners manual is there a fuse listing for voltage regulator or alternator or charging circuit or some such.
Strangely enough the wiring diagrams for my 97 Explorer call this fuse “generator/voltage regulator.”
Tradition i guess.
If this fuse is blown the alternator wont charge.
Ditto to what Joseph sez as the voltage will spike when the batt cable is removed while running. Not good.
My husband ran a scimatic (sp) of all the fuses there all ok.I will tell him never remove the cable off the battery again while the car is running.Like I said he knew it was a bad ideal I dont know why he did it.Can a short in the raido cause the battery to run low?
That fuse that I mentioned provides excitor voltage to the alternator. Without this voltage the charging process cant begin.
I’d check for this voltage (12 volts)at the fuse & alternator.
I have no idea how your X-tera is wired but on my 97 Explorer, this voltage is supplied from the starter relay & the fuse is under the hood.
Hope this helps & good luck with it
I called my husband and read to him what annymous wrote,when he gets off work he going to go the his friends macanhic shop and check what you said.
The battery should give a 12.6 volt reading when the engine is off, and in the 14 or so range when running.
Are you saying that the 11 volts is with the engine running?
With the key in the RUN position does the little red dashboard ALT or BATT light come on? If not, there is your problem. Battery voltage must be provided through the bulb to do what is called “excite” the coils in the alternator.
Bulb burns out, alt. does not work.
The battery light comes on when I turn the key over same with all the lights ,then of course they shut off so we suppose the lights works. Yes the battery reads 11 volts when the car is running,belts, fuses new battery new alternator and the car is still running at 11.
I would suggest checking the output voltage of the alternator at the main power lead at the back of the alternator.
If the voltage there is 13-14.5 volts and the voltage as tested at the positive battery terminal is 11, then I would suspect a wiring problem.
I do not have a schematic for your car, but my guess is that there is a fusible link in the line between the alternator and battery. If so, this should be located near the battery positive terminal and will resemble a short length of wire, possibly with a connector on each end.
Another possibility could be that the link is a plug-in type and may be located in a fuse/relay box.
Hope that helps anyway. 
Check the voltage on each of the alternator leads with reference to ground. They should be close to the battery voltage. If you find one that is low then that is the lead that has the trouble on it.
Since you stated that the warning light comes on with the ignition on that is good. There still may be a problem with that connection to the alternator though.
The problem here may be a bad connection between the alternator output lead and the positive battery lead. The voltages should be very close to each other while the charging system is running. Another way of testing the link is to measure the voltage between the two points. There should be less than 0.1 volts between the points.
I am pretty sure thats what my husband is checking next he just took my car to his friends auto shop.Will let you know
Well I appricate all the help I received here …We did find the promblem it was a bad Voltmeter ! I called my husband at the auto shop and asked him to use a new voltmeter and my car read at 14 just where it should be…Sometimes the answer is as plain as the nose on our face. Again thanks to all of you who took time to help me slove this promblem, next time ask if they have a good working voltmeter first…Thanks
You’re welcome for the help and thanks for the update.