Summarizing how to troubleshoot your "slow-crank" condition:
1. Inspect the battery post connections to the battery cable terminals. If needed, remove terminals and clean the battery posts and cable terminals. Re-install cables to battery (Positive RED cable first, then Negative BLACK cable and look away from the battery as you place the cable on the NEG post).
2. With the ignition key removed from the ignition switch, check the battery voltage with a voltmeter. You should read over 12 Volts DC. Typical voltage is around 12.5 to 12.7V. Less than 12V? Your battery requires charging before continuing troubleshooting.
3. If you have 12V+, one additional voltage check between the NEG battery post and the starter relay main terminal should reflect the same voltage.
3. Now you should have a charged battery, good connections, and 12V+ to test the cranking voltage. Attempt to crank the car and listen to the cranking speed while simultaneously checking the battery voltage again with the voltmeter. The starter/engine load will draw down the battery voltage from 12+ V by two or more volts. This is normal and the battery should not drop below 9 to 10V. If it hits 8V or less, your battery is likely the problem and going bad. If the voltage is good enough to get the car to start, you should see the voltmeter change to approximately 13.5 to 14.7V as the alternator begins charging the battery.
4. If you experienced the slow-cranking again and the battery voltage was 9 to 10V, your starter, starter relay, and/or starter cable wiring should be inspected/checked to see why the starter is spinning slower than needed to start the engine. Good cables and connections should be ruled out before removing the starter.
5. It is a pain to do but removing the starter and having it checked under load at the auto parts store will let you know if the starter is bad. DC electric motors draw more current when the armature windings are hot but the slow-cranking condition can only be remedied by checking all of the starting electrical circuit.
BATTERIES
There are three major manufacturers of automotive batteries in the U.S., all auto parts suppliers source their batteries from these three companies: Exide, East Penn, and Johnson Controls. The Walmart EverStart batteries are made by Johnson Controls and are economical and great quality.
If you are concerned with originality, you could purchase a reproduction Mopar battery in Group 24 (smaller) or 27 (larger) which have been updated to Absorbent Glass Mat (AGM) versus standard lead-acid. These are very pricey at well over $300 if you can even find one in stock.
Another option is to buy a plain-looking battery and add a "Battery Topper" which looks like the top of an original Mopar battery with the appropriate yellow/green/red battery caps. The toppers are still available and that is what I run on a SuperStart battery which is manufactured by East Penn. I also added an incorrect but cool Mopar decal to the side of the battery that fools most people (see pics).
There are also kits available to add only the plastic battery caps to a plain battery that has the six standard battery cap holes but that can be more difficult to get right and will not have the Mopar raised lettering on the battery top.
Good luck on the troubleshooting. Let us know what you find.
