Does leaving the car unlocked drain the 12V battery?

[MurphNMagT]

2021 CX-5 Touring. If the car is left unlocked (in a garage) and the key/fob is far enough away that RF communications are not possible; will the drain on the car's 12V battery be greater than if the car is left locked?

I have read about this elsewhere with other cars. I was on an HRV forum (don't worry guys, my lady has an HRV, my own CX-5 is going nowhere) and read a couple comments saying the car's battery drain was somewhat higher -- than, you know, the standard drain from modern cars full of computers and 'connected services' etc. -- when the car was left unlocked. No additional context or explanation.

My 2021's 12V battery is not in bad shape and I'm maintaining it but is probably on the downslope towards its retirement, and I'm trying to do what I can to extends its ever shortening life. I suppose that just changing my habit, to locking instead of unlocking, is no big deal, but I am somewhat more curious than anything. I can see from the manual there's a number of ways one can alter the function of the key/fob, buttons, and I don't believe I've ever done that.

Thanks!

 

[wlong01]

I leave both our CX-5's unlocked in our garage and never had a problem plus the fob's are in range since I can lock/unlock the doors from inside the house.

Not sure why unlocked doors would put more of a drain on the battery.

 

[madar]

I saw it on another forum from a Mazda tech a few years back, don't know if it's true or true for the newer models.

 

[Mazdiod2]

Maybe their rational that the battery drain is higher because the system is in a higher state of 'alert' has some merit.
I think the best way to keep your battery going is a battery maintainer. You can plug one into the 12v lighter jack.

 

[N7turbo]

In my experience, no. Even if the doors are open (provided you turn all the lights off).

 

[paris1]

In my experience, no. Even if the doors are open (provided you turn all the lights off).

Really? This thread is getting stranger with every post!

 

[N7turbo]

Really? This thread is getting stranger with every post!

Yeah, you can get the car to go to sleep with the doors open.

 

[hsdejong]

You can plug one into the 12v lighter jack.

My CX-5 2023 (European) has three lighter jacks. All of them are switched off when the car is switched off.
Only the OBD2 connector is connected all time to the car battery.

 

[GrampaSlade]

There is no "normal" reason for a battery to drain while sitting in a garage

 

[ceric]

The keyless entry unit/sensor is constantly probing for fob response. (even when it is unlocked)
(so that when you press the rubber button on the handle, it locks)
Usually, a small part of circuit is always awake to interact. (in circuitry, it is call always-on.)
That consumes some power. Should be less than 0.1A (or 1.2W)

 

[hsdejong]

There is no "normal" reason for a battery to drain while sitting in a garage

"Normal" or not, but modern cars like the CX-5 always draw a small current (approx. 0.06A) from the car battery to keep some electronics like the keyless entry and burglar alarm alive.
Hour after hour, day after day, this current will drain your battery in about 6 weeks.

 

[ceric]

My daughter once left her Mazda3 on roadside for the summer and came home by air.
After 2 months, the battery was dead.... A Li-ion jumper I bought her saved the day.

 

[cz5gt]

Not for few days or even a month if at near full charge. No issue there.

But on avg after 2-3-4 months the battery would drop though (newer cars have electronics that dont fully shutdown) and needs refresh.

Thats my observation

 

[GrampaSlade]

"Normal" or not, but modern cars like the CX-5 always draw a small current (approx. 0.06A) from the car battery to keep some electronics like the keyless entry and burglar alarm alive.
Hour after hour, day after day, this current will drain your battery in about 6 weeks.

I would posit that any car battery will drain after 6 weeks of non-usage.

 

[hsdejong]

I would posit that any car battery will drain after 6 weeks of non-usage.

A healthy normal lead acid battery will self-discharge at about 5% per month.
Theoretically, it would take 20 months to fully discharge.

 

[N7turbo]

The keyless entry unit/sensor is constantly probing for fob response. (even when it is unlocked)
(so that when you press the rubber button on the handle, it locks)

Can this be proven? I don't think a signal is sent until the button is pressed.

It has to "listen" for a FOB, but it is not broadcasting.

 

[cz5gt]

there are certain zones near the car yes (documented in the manual too) but whether that affects the power consumption I dont know. I can measure next time. I have measured unlocked but idle after 15 min and its bare minimum.. something like 50mw if i recall

 

[hsdejong]

50mW divided by 12,5V is 4mA.
Or did you mean 50mA?

 

[Conrad 16.5]

The keyless entry unit/sensor is constantly probing for fob response. (even when it is unlocked)
(so that when you press the rubber button on the handle, it locks)
Usually, a small part of circuit is always awake to interact. (in circuitry, it is call always-on.)
That consumes some power. Should be less than 0.1A (or 1.2W)

The system doesn't wake up till an action is taken. Either the action buttons on the car or a fob button press. The car 'listens' for a signal from the fob (button press) and uses power for that. Of course, it also listens from an action button press.

If you press an action button on the car, it polls the fob (sends out a signal), and if the fob returns the correct handshake, the doors unlock.

If you press a button on the fob, it sends out a signal to the listening car, and if all is well with the signal, the car unlocks.

Lots of folks believe that the fob is always transmitting. From an engineering standpoint, that make no sense. Why would it do this and drain the battery unnecessarily? No need to transmit all the time. That's what the buttons are for.

 

[Conrad 16.5]

"Normal" or not, but modern cars like the CX-5 always draw a small current (approx. 0.06A) from the car battery to keep some electronics like the keyless entry and burglar alarm alive.
Hour after hour, day after day, this current will drain your battery in about 6 weeks.

I've gone on vacation for 6 weeks many times and come back to my CX and it started right up, no problems. I didn't have it on a tender either, although I do use a tender on all of my cars regularly.

During the year I always move the tender around between all of my vehicles. I keep it on one vehicle for 5 days or so and then move it to the next. With several vehicles in my garage, I don't always get a chance to drive them enough.