Problems with poorly charging the 12-volt lead-acid battery in the CX70 PHEV

[ianwh4]

Twice this winter in Michigan, my CX70 PHEV's engine's 12-volt battery had a "total" loss of power. This typically occurs after a few short excursions under 19 miles, followed by recharging the PHEV battery to fill it up. Basically, it's a time when the petrol engine isn't used for more than a few miles at a time so the alternator can charge the 12-volt battery. Both instances occurred in the morning following an overnight charge of the PHEV. The next day, upon pressing the start button, I discovered that neither the red security light nor any of the instrument cluster lights were illuminated. Additionally, when left unlocked, the door locks do not make a sound. Sitting quietly while attempting to press a start button that is not illuminated. Approximately 2.77 volts was the reading I got the second time I lifted the hood to check the battery voltage. In all likelihood, it is a weak battery that has trouble charging. While the first attempt at connecting a battery charger brought the voltage closer to 8 volts, the second time around I heard a lot of noise coming from the engine area and had to turn off the device. They jumped me using Mazda Roadside Assistance. The vehicle was able to be restarted by connecting to their tow truck and performing a classic parallel jump. Got it going and dropped it off at the local M-dealer for analysis today. Findings are still being finalised.

Has anyone encountered a situation like this before?

[TDudette]

Weak 12V power source. Less time to charge due to chilly weather and shorter journeys. Probably the dealer will swap it out for you.

[TDudette]

🫠

[ianwh4]

Just wanted to give you a heads up regarding the 12V battery not getting charged enough from just using EV mode for short trips in the winter. The vendor connected it to their charger and battery testing apparatus. Instead of replacing it, they fixed it under warranty and didn't charge me a dime. The dealer's mechanic suggested using a battery tender to charge the 12-volt battery if you plan on continuing to drive short distances (<20 miles) on electric mode only.
The other models are around 1.5 amps, but I'm inclined to go with a 'Battery Tender' 4 amp type. It would make me very delighted to hear your comments on that.
Note: the tow truck connected its 10-foot charging cables to the 12-volt battery's positive terminal and the frame's ground terminal after I connected five feet of my own cables to the battery. It was immediately jump-started, and I backed it out of a cramped garage and drove it to the dealership. In Michigan's 0-20F winters, the lessons learned from using the EV mode are invaluable, but I still adore the car.
 

[ianwh4]

Also, I'm starting to lean toward the "short trips" side, so I appreciate your perspective. They put it on their charging system yesterday afternoon, so we should receive the findings sometime this morning.

There is a lot of helpful information that owners find on our site, so I appreciate you taking the time to weigh in. As far as I am aware, the battery compartment has the tiniest cargo area of any place I have ever seen.


Just to follow up — Is the 'battery tender' or trickle charge mechanism something you're familiar with? If so, which model/brand do you think is best?

I intend to start checking the voltage at regular intervals from now on.

However, I really enjoy driving this vehicle and would like to ensure its dependability to the best of my abilities.