Ive got a slow crank on my 5.7 v8 350 . I doubt its the starter and i may or may not have a bad ground somewhere? Other than that im bulking high as fuck carbs and water
1) Measure battery voltage when the car is off. Determines if the battery is charged.
2) Measure the battery voltage when the car is on. Determines if the alternator is working.
3) Take the battery leads off and look for corrosion or oxidation on the terminals or inside the clamps. Clean if necessary.
4) With the negative cable still off the battery, check the resistance between the cable clamp and any metal part of the frame. Should be a few ohms at most. Determines the ground integrity.
5) Check the terminals of the starter motor. If they are corroded, clean them. Determines if you have a bad connection to starter.
6) If none of these is problematic, then a CCA test next.
9/10 it's #3 - corroded battery leads.