I had the same question on my 2019 Signature. The response that I received from Mazda was CCA of 356. Here is the full reply:
Thank you for contacting Mazda Customer Experience Center! We appreciate you being part of our Mazda family, Jim, and I hope you are enjoying your CX-5 so far.
Your vehicle’s OEM battery that was installed at-factory was manufactured in Japan. Rather than a CCA rating, Japanese auto battery manufacturers use a JIS (Japanese Industrial Standards) to identify a battery by its capacity (amps), dimensions, and battery terminal arrangement by using a six-digit alpha/numeric number. The battery for your vehicle uses JIS 55D23L. Based on my research, this would convert to a CCA rating of 356. For your records, the original part number for your battery will be F221-18-520F.
Please do not hesitate to reconnect with us if you have further questions. You can reach me directly by replying to this email or using the number below. Thank you again for contacting Mazda, Jim, have a great day!
Sincerely,
Kailey
Representative, Customer Experience
800.222.5500
Select Prompt 2, then Ext. 1168
Office Hours: Monday - Friday 6:30 AM - 3:30 PM Pacific Time (SR Number: 1-2374083689)