I have an 03 Chev malibu. I just put a new battery in it. She won't start without a boost.runs fine afterwards.if I let her sit for a bit I will need a boost again..please help

New battery could be faulty or alternator not working.
If nothing happens when you turn the key,to check battery to determine its state of charge. Many starters won't do a thing unless there is at least 10 volts available from the battery. A low battery does not necessarily mean the battery is the problem, though. The battery may have been run down by prolonged cranking while trying to start the engine. Or, the battery's low state of charge may be the result of a charging system problem. Either way, the battery needs to be recharged and tested.If the battery is low, the next logical step might be to try starting the engine with another battery or a charger. If the engine cranks normally and roars to life, you can assume the problem was a dead battery, or a charging problem that allowed the battery to run down. If the battery accepts a charge and tests okay, checking the output of the charging system should help you identify any problems there.
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Engine Won Crank or Start