1996 Dodge Ram 2500 battery died when I left lights on.charged battery.truck starts up but wont stay running when I let off the gas.when I used to start the truck it would have a high idle

 

If you suspect no problem in your idle air control valve, then have the battery tested. Sometimes a deep cycle discharge of a battery puts it over the edge if a cell is weak and it goes bad. The engine dies, because it needs a good power source, even at idle and the alternator is expending lots of amps to recharge a battery that won't hold a charge and nothing is left for normal operations until the alternator is turning fast enough.