I have a 2021 Mazda CX-5 non-turbo, in-line 4-cylinder, automatic transmission with about 85,000 miles. I drove the car this morning with absolutely no trouble - nothing out of the ordinary. I parked it in the driveway when I got home and went about cleaning up the interior, vacuuming the floorboards, wiping down the seats, dash, and console, and cleaning the windows. When I finished, I went to put something in the back and the hatch would not open. Not even a beep.

I checked to see if the doors were locked and the button on the key fob did nothing. I tried using the door lock switch on the driver's door and there was no response. No lockey, no unlockey. Further investigation revealed that not a single electrical control in the car is working. The lights don't work, nothing. The only thing I can find on the car that is working right now is the security system activated light on the instrument panel. It's flashing every 2 seconds, just like it normally does when the engine is off. Beside that, when I push the start switch with the brake pedal down, nothing happens; but when I push the start switch without the brake, the green light on the start switch illuminates for about a second or two, then nothing. Nothing else works.

I tried disconnecting the negative terminal on the battery for about 15 minutes. I reconnected it and there was a beeping inside the car for several seconds, but no other indications on the instrument panel or anywhere else. No response from any controls. I tried disconnecting the negative cable again and reconnecting it, and got the same reaction.

Does anyone have any idea what might be going on with this car?

 

First DONT DISCONNET THE BATTERY in the future it does nothing and most of the time and could cause other issues.
This is an old MYTH started years ago, like pre 2001.

 

So, just as a matter of covering all the bases, I checked the battery voltage - fully expecting it to be normal (between 12 and 13 volts. It was 4.71 volts! I couldn't believe it! The car started and ran fine all morning. We made at least three stops and there was never an indication that the battery could be weak. But it was toast. I tried putting my battery charger on it for a while and got it up to just over 12 volts, but as soon as I tried to start the car, the battery died. I checked the voltage again and it was lower than before.

I don't think I've ever seen such a sudden, catastrophic battery failure. I even had a battery swell up and spew sulfuric acid once, and was still able to get it to the battery shop after jumping it off. When I pulled the battery out of the CX-5, I could see the acid level through the white casing and it was less than 2/3 full. It was dry on the outside and I didn't see a leak, but it went somewhere.

My guess is the computer shut itself and everything else down as an automatic protective measure against the low voltage. (Lesson learned.)

I guess I got all I could expect out of the stock battery (which was, incidentally, a Panasonic - I didn't know they even made car batteries!). I put a new battery in it and it seems to be fine. Time will tell if the old battery just wore out or if something else caused it to go bad. I don't guess it would have kept running at under 5 volts if the alternator's bad.

I'd appreciate any thoughts on any possible causes.

 

On modern cars that's how they go out a lot of the time, due to the complex amount of electronics that rely on them. If it was the original battery, you did well with 4-5 years and that many miles on it.

 

Electrical issues can be some of the most frustrating and puzzling issues to investigate and solve.

Best case scenario? The vehicle is 2021, it's now 2025, the battery could've simply been at the end of its life. The morning drive may have allowed the alternator to keep the system charged just enough to get around but on the brink of failing.
Less-than-best (worst) case? a combination of failing battery failing alternator / charging system / corroded, damaged wiring / costing more to repair.

I believe acid inside a battery can be "evaporated" by ionization from an alternator working extra hard (over charging) to energize. Might explain lower fluid levels.

I'm sure you'll monitor regularly, check voltage etc and certainly notice if electrical system goes dark again. If so after a new battery then, obviously it's a deeper issue.

Please follow up here. I'd be curious to see what you discover.

 

The picture you paint tells me the battery was on it's last legs and the time you had the doors open vacuuming and detailing was enough to kill it. Being a sealed battery they still use up the electrolyte over time at a much slower rate but I would still check the charge voltage even if there are no other signs of overcharging.

 

You're lucky your OEM battery lasted that long.
Mine lasted about 13 months (cold weather) and I replaced it with "real battery".
Even with a "real battery", most modern vehicles will normally get only 3 years before they start failing again.
It can be slow or catastrophic as you found out, which is why it is best to load test your battery every year.

Real Battery: meaning a highly rated and tested one.

 

I am very doughtily that that was the original battery. Please provide a picture when you remove it of the brand name and complete serial number that is cast/melted in the top portion and on the side of the battery.

But I do agree that it sounds like your battery and possible the connect ability and the condition of the battery (load test after full charging) was the descriptive issue that should be looked at first before anyone should be making any kind of conclusions.

 

Out of curiosity, why would you doubt it was the original battery? Panasonic is the brand Mazda uses at the factory (just changed my '21s original battery a couple of months ago- and with this post I am glad I did!). I would venture a guess the vast majority of 21's are still on their original battery. Most folks don't do any kind of maintenance/checking of their battery until it becomes an issue.

 

Panasonic is carried at many dealerships parts departments (NOT ALL) also sold retail in many authorized retailers and often changed by dealerships from them going bad sitting in the lot prior to a sale and not recorded or required to be recorded by Mazda crop from the dealership. This is also why on this forum alone we often see members reporting not having the original battery when they look. A dealership is NOT required to replace a battery with the factory original brand only the minimum require specification of a battery. Knowing the exact service life of a battery can help diagnosis issues as well as give some hints to possible future problems. We replace over 500+ batteries a year and I often hear and read on forums claims of unusual not normal longevity of battery service and when we look at the serial numbers we find a different story.

You are absolutely correct in that the average owner of a vehcle never checks or has checked their battery every season change or until they like you have an issue?

Btw unless you took the serial numbers from your battery (why would you) you really don't know if it was the original factory installed battery. And this subject has come up a few times on this forum.