I second this. I had to replace my battery cables from the battery down to the starter. My starter gear would pop out and stay out while I was driving because the wires were corroded and not giving the starter the proper voltageIn addition to following Logan's advice, check the simple things, especially neglected battery cables. Disconnect the cables, then clean the terminals and battery posts with a battery cleaning tool. This is also a good time to clean any corrosion in and around the battery. Baking soda works. Finish up by spraying the terminals with corrosion protectant.