I have a 1999 jeep Cherokee 4.0 liter inline 6. want crank so jump off. gauge on dash is showing not charging do that mean alternator bad light very dim.
More likely a toasted battery. Get a free check at may auto pars stores.
Your best bet is to remove the alternator and battery. Take them both to your nearest McParts store where they will charge and test the battery and test the alternator.
McParts = any chain parts store.
Get it started and measure the voltage at the battery. It should be about 14.5 volts or maybe even a little higher with a low battery if the charging system is putting out what it should. If it is 13 volts or lower, your charging system is either weak or not functioning. It would also be good to fully charge the battery and have it load-tested. Even with a full battery in good condition you should not see the voltage dip under 13 volts with the engine running. And a good, full battery should have a voltage of about 12.4-12.6 volts with nothing drawing from it. (engine and all accessories off)
Repeated running low or dead of a lead-acid (car) battery will kill even a brand new battery in short order. A battery that won’t take a charge puts tremendous stress on your charging system, and a weak charging system stresses your battery. Both must work in concert with each other. Also make sure all your battery connections are clean, tight, and in good condition. Poor connections, low batteries, and failing charging systems can also wreak havoc with the electronics on your car and cause all sorts of random drivability and other problems too, which will likely go away when the power issues are addressed.
I’m not sure at what voltage the “battery” light on your dash is calibrated to turn on at. I would suspect that the threshold would be at a little under 13V with the engine running. Usually the battery light coming on means you either have a weak or dead alternator, inoperative voltage regulator (which is in the car’s PCM on most recent cars), or problems with the wiring. Normally a bad battery doesn’t make the “battery” light come on unless the charging system is bad or severely overtaxed, such as having a bad battery and running all your electrical accessories. (I know this is counterintuitive)
They both need to be tested. I’ll bet they’re both in need of replacement. Follow Rod’s advice.
But before you do, look up the proper procedure for removing and replacing batteries. Lead-acid batteries outgas hydrogen, and producing sparks around hydrogen by not connecting the battery cables in the right order can be very dangerous. And, just in case of an accidental spark, wear eye protection and leather work gloves. If you have a full face shield, that’d be even better.