Faulty Battery Post Connections
If the battery itself is in order, the loss of power may be caused by faulty connections between the battery and the starter. The ‘post’ connections on top of the battery are always suspect. In extreme conditions – icy weather for example – a starter motor can take 400 amps to turn the engine over. Any faulty connection will prevent such currents from flowing, but may nevertheless pass the much smaller currents demanded by the ignition lights.
A quick clue as to the condition of the connections can be had by touching the positive terminal of the battery, marked +, immediately after you try to start the car. If it feels hot, the connection is poor.
Corrosion may have begun on the inside of the clamp, on the post or both. A quick whisk with some sandpaper will restore the surface condition of both.
Battery clamps often become slightly oval inside due to corrosion. So when you replace the clamp try to place it in a slightly different position so that it presents a fresh face to the post.
With the ‘helmet’ type of connection, a screw through the top locks the connection in place. If it has worked loose tighten it, but if this reduces no result, remove the screw, lift off the ‘helmet’ and clean it and the post with emery paper.
If the battery connection will not come away from the post after it has loosened, trickle hot water over it. Never try to pull or twist it free as this risks cracking the battery case.