I was not wild about the design of the RX-8 positive battery terminal. It distorts easily and can become difficult to tighten sufficiently, particularly if over-tightened or taken on and off the battery repeatedly. The new Mazda part is around $35 shipped as of this writing. I did a little research and found this Toyota positive battery terminal that is a little less expensive at about $25, and in my view it is a superior design. It has reinforcement at the top front of the ring near the bolt to prevent distortion.

The Toyota part number is: 90982-05058. Terminal Assembly.

It seems to fit perfectly.

Remember that positive and negative battery terminals (posts) are different diameters.



Orignal Terminal


Toyota Terminal installed

 

I recently bought these.





A tightening wedge design on the terminal and nut on top is the best design I've seen.
It's only been a year so far, but if they fail somehow, I'll post it.

 

On the Advanced Auto wedge DieHard terminals, note the lip behind the rear screw post on each of the terminals that looks like it might prevent the cable end from laying flat and having the designed contact area. If using these Advance Auto DieHard posts with the factory RX-8 cables and ends, one might file down that tab.