MHEV battery issues? Extended warranty?

[stw]

Good morning. We are considering purchasing a 2025 MHEV CX-90. I've browsed other forums, and see a good number of posts about the MHEV 48v battery issues that necessitate a replacement. Have any of you had this issue?

We usually don't buy an extended warranty, but are thinking about it for this purchase. Seems that Mazda fixed many issues from the 2024 models, but it looks like there are still some growing pains. Do you all have suggestions on the best place to buy a true blue Mazda extended warranty/service contract?

Thanks!

 

[Boland01]

Following

 

[taran1900]

I have a CX-70 Turbo S with about 9k miles. Have had no battery issues at all. I did get the extended warranty because it's still a totally new design.

 

[RobertJT]

The minority of failures have been with the PHEV lithium ion battery. The car basically runs on the Lithium Ion battery and it gets recharged by the 4 cylinder engine. If the battery fails the car is not driveable. It does not appear to be a frequently happening but naturally those who experience a car that just dies and has to be towed will be just as upset.

What has been failing in large numbers is the flooded lead acid 12 volt battery in the MHEV. Mazda thought that they could get away with a cheaper flooded battery since the Lithium Ion battery was being used for restarts with the ISG system. What they failed to take into account is the 12 volt battery also supports the rest of the car with air conditioning, heat, head lights and all the computer modules during a IGS shutdown. The voltage droop wreaks havoc with all the electronics. Mazda's answer has been "you're not driving the car enough and as a result you the customer get to buy the new battery". A quality AGM battery would have been a better choice so that's what everyone is buying when the OEM battery craps out.

There are a bunch of people including myself ranting and raving about having to replace a battery in a 6 month old car with what should have been in the car to begin with. The car came out in late 2023 so all the CX-90s are less than 2 years old. No battery should be failing that early.

 

[Antoine]

The minority of failures have been with the PHEV lithium ion battery. The car basically runs on the Lithium Ion battery and it gets recharged by the 4 cylinder engine. If the battery fails the car is not driveable. It does not appear to be a frequently happening but naturally those who experience a car that just dies and has to be towed will be just as upset.

What has been failing in large numbers is the flooded lead acid 12 volt battery in the MHEV. Mazda thought that they could get away with a cheaper flooded battery since the Lithium Ion battery was being used for restarts with the ISG system. What they failed to take into account is the 12 volt battery also supports the rest of the car with air conditioning, heat, head lights and all the computer modules during a IGS shutdown. The voltage droop wreaks havoc with all the electronics. Mazda's answer has been "you're not driving the car enough and as a result you the customer get to buy the new battery". A quality AGM battery would have been a better choice so that's what everyone is buying when the OEM battery craps out.

There are a bunch of people including myself ranting and raving about having to replace a battery in a 6 month old car with what should have been in the car to begin with. The car came out in late 2023 so all the CX-90s are less than 2 years old. No battery should be failing that early.

Great to know, thanks for posting those insights! Has anything been done to the 2024 and or 2025 models to resolve these issues?

 

[RobertJT]

Great to know, thanks for posting those insights! Has anything been done to the 2024 and or 2025 models to resolve these issues?

Recently there is a software update/recall for the MHEV that changes the threshold for generating the alarms. I don't know if that just hides the issue. My battery just died in December. I replaced my flooded with an AGM type and that solved the problem for me. Been fine for the last 5 months. Mazda's earlier solution was to disconnect the battery to reset the BCM and ECU. That would get rid of the messages and alarms temporarily.

 

[RobertJT]

It is now August 2025 and the car was used on its first road trip. 800 mile round trip. No issues. I wonder what happens if the L.I. battery fails in a MHEV. Can you still drive the car with the ISG turned off?

 

[RobertJT]

Battery change to Group 35 AGM

Supposedly Mazda has authorized the dealers to install AGM as replacements if the OEM enhanced flooded battery fails. This is to be covered by the cars warranty. There is no recall at the moment so if yours is still working they won't change it. They finally reimburse me for the one that failed in my car back in January of 2025. They had been using telematic data to deny warranty's on batteries claiming the data indicated we were not driving the cars properly. The NHTSA might step in after a couple of CX90s and CX70s shut down and crashed because of battery failure. They get involved when there is a safety issue.

It's funny. Mazda usualy volenteers the information to the NHTSA when there is a safety concern. Not this time around. They are being dragged kicking and screaming. Must be an exec who told the pee-ons to use those old batteries kicking around in the warehouse. After all what could happen? Notice if you watch the video the replacement is a Mazda brand AGM battery.

https://www.copart.com/lot/81011415/2025-mazda-cx-90-premium-fl-orlando-north