clip voltmeter leads directly on the battery posts (not the cables) and hit the starter button while watching battery voltage readout. if the voltage stays roughly the same the battery is fine and the issue is farther along; next move the voltmeter leads to the battery cable ends and try again. if it reads different than at the posts themselves you've got a poor connection at the cable ends. A really quick way to eliminate battery or cable connections. Any further down the line you'd just have to follow the positive cable end through the solenoid, then the starter motor lead. Any help???

Mike