My pontiac g5 2009 problems with it starting randomly

Use a voltmeter to measure from the battery negative post to a good ground point on the engine (alternator bracket or case.) It should read zero volts during the starter click. Any reading tells you there is a bad ground connection somewhere. Bad grounds can be affected by weather. Also, during click-time, measure volts between battery positive and good-ground. It should not drop below 11 volts. Low voltage could be starter or battery, so measure the positive volts when you turn on the headlights. It should not drop more than one-half volt.