Hard Cranking When Hot

While pondering if the battery or cables is good for possibilities. A simple voltmeter check while cranking provides usable information.

Voltmeters draw very little current, so leads can be extended to measure voltage drops in cables, and other places, like at starter, at remote location so you can see while cranking.

Starter motors are DC motors. The maximum torque is when they are stalled, but it is limited by armature current. Neglecting losses, the peak power is volts times current. So with poor connections, current is limited, and voltage is reduced, hence less power to crank at starter motor.

Acceptable voltage drops are a few tenths of a volt, more than that, is a problem. The voltmeter provides a way to evalutate, and improve connections.

If you have lead lugs, consider changing to crimped copper. Welding cable may not meet all the specifications for automotive starter cables. It has fine strands, if oxidized it may not be possible to make good connections.