98 Jeep wrangler with a battery that won't charge
 

I was hoping someone could help me out hear I have a 98 jeep wrangler
that won't charge the battery. so I thought it must be the alternator
so I had it checked at auto-zone but they said it was okay and the
battery seems to charge when you charge it with battery charger so I
think the battery is fine any ideas would be greatly appreciated.