Considering that a modern battery runs about $150, and a cable costs about $12, replacing a battery and/or a starter before testing the battery cables can be a costly lesson in diagnostics.
Q. I have a Ford pick up truck that is about 15 years old and sometimes it just won’t start acting like it needs a battery or a starter. The battery is about six months old and the starter is about a month old. I have cleaned the battery connections as well as the starter connections.
Where is the problem and how do I fix it?
A. I would take a very careful look at the battery cables.
The battery cables travel under the engine and can be exposed to all kinds of corrosive materials causing high resistance and poor connections. Cleaning the battery cable ends won’t solve the problem if the cable is compromised in the middle.
This was very common on some Ford trucks where the negative battery cable attached to the frame of the truck and then terminated at the engine block. You can test for voltage drop with a digital volt meter measuring from the negative terminal to the engine block ground.
This video explains how the voltage drop test works:
If there is a reading of more the .3 volts the resistance is high and causing the problem with hard starting/cranking. If the readings are high replace the battery cables and your problem should be solved.