How to attach a BM2 battery monitor to a Skoda Karoq battery?

[Mark-Surrey]

Hi.  Hoping that somebody might be able to help me.  We rarely use our Skoda Karoq any more, so it spends a lot of time in the garage.  A couple of weeks ago I got lots of different warning messages pop up on the screen when I tried to start it.  So I called Skoda breakdown assistance.  Within minutes of arriving, they diagnosed the problem as being a low battery (which interestingly, seemed to be the only warning message which was NOT popping up on the screen!).  I heard lots of good things about the BM2 battery monitor, which you just connect to the positive and negative terminals of the battery, and you then connect to it using bluetooth on your mobile phone, and use an app to see the state of the battery, get warning messages when you're near the car if the battery is low etc.  So I bought one of these BM2 devices, and I tried to install it today.  I was able to fit one of the BM2's terminals to the Karoq battery terminal which is closest to the front of the car, by loosening the nut on the battery sufficiently to slide the terminal of the BM2 into place and then tightening it again.  But I just couldn't figure out how to attach the other BM2 terminal to the Karoq battery terminal which is furthest from the front of the car.  I loosened the nut, but there is a formed metal piece which prevents you from sliding anything in behind the nut.  The clamp of the battery lead seems to be sprung so that it pushes the nut against this formed metal part.  Do I have to completely disassemble this clamp component?

 

I was hoping to not have to completely disconnect the battery, but ended up loosening the nut that it disconnected anyway.  I then got all kinds of warning messages when I tried to start the engine again.  Fortunately I remembered what the Skoda breakdown assistance guy told me a couple of weeks ago.  You have to turn the steering wheel as far as possible one way and then the other, in order to reset these warning messages.

[Breezy_Pete]

Is there enough thread to just fit the terminal on top of existing nut and then add another nut?

Photos would help us understand the problem.

Edited 11 November, 2023 by Breezy_Pete

[J.R.]

Talk about an over-complicated self defeating solution which will significantly increase the parasitic battery drain and hence further reduce its autonomy 😒

 

Why not have an LED voltmeter plugged into the cigarette lighter socket or a fixed one tapping off its wiring like I have? One glance through the window tells me the level of charge.

[Breezy_Pete]

An LED voltmeter will take many more mA than the 1 that this claims to.

Might add one to my Amazon wishlist for my spare car.

[Mark-Surrey]

1 hour ago, Breezy_Pete said:

Is there enough thread to just fit the terminal on top of existing nut and then add another nut?

Photos would help us understand the problem.

Thanks for the tip! I don’t know why I didn’t think of that in the first place!  I had a spare M6 nut in my garage, which I used to attach the BM2 terminal. 
 

There’s a plastic flap over the positive battery terminal, and I had to cut into that with a Stanley knife and fold it back a bit, in order to make room for the BM2 terminal to protrude. It’s all working fine now. Once I had actually attached the terminals, it was literally a 2-minute job to download the app, and connect to the BM2 via Bluetooth.

[Breezy_Pete]

If I do get one I may extend the wires and mount it in the cabin, as the Bluetooth range will probably be better when not in a closed engine bay.

I'll be interested to hear how close you need to be with your phone to get data.

[J.R.]

1 hour ago, Breezy_Pete said:

An LED voltmeter will take many more mA than the 1 that this claims to.

Might add one to my Amazon wishlist for my spare car.

Good to know.

 

But 1ma only for remaining in standby waiting for a Bluetooth connection and also when communicating data sounds implausibly low for a mobile phone comms device.

 

The original LED voltmeter I had took IIRC 3ma but it had an on/off switch which I would use if I knew the vehicle was going to be left for a long time.

 

It was shonky though and the soldering holding the USB socket to the PCB fractured and was irreperable, the new one has a circular array of red, orange and green Leds with some tiny illegible markings of the corresponding voltages, I think the fag lighter feed must go through a diode as the indicated voltages are always between 0.7 and 1.0v less than the actual battery voltage.

 

The unit sounds interesting for those who never look up from the screens of their mobile phones, I just want to see the voltage by looking through the window, if its too low then I charge the battery before starting the vehicle, I have regrettably shortened the life of my current battery by cranking once when the voltage was too low after leaving the sidelights on, this was when the voltmeter was broken.

[J.R.]

I can see uses for it though especially on standby batteries, my caravan lead took on water during these biblical rains and tripped the RCD switching off everything in the house including the freezer, I was unaware in the caravan because everything is 12v, the only warning I would have got would have been the computer battery getting low, the battery was still at 12.3v so no damage was done but it could have been expensive, that device would have been a good thing to have.

[Mark-Surrey]

47 minutes ago, Breezy_Pete said:

If I do get one I may extend the wires and mount it in the cabin, as the Bluetooth range will probably be better when not in a closed engine bay.

I'll be interested to hear how close you need to be with your phone to get data.

I’ve just tried it. Our Skoda is at the far side of our double garage. It didn’t connect when I was outside the garage at the opposite side. But it connected as soon as I opened the garage door (regular door, not where the car itself goes in and out). I measured it with my laser device, and the car bonnet was about 7.5 metres from where I was standing.

[Breezy_Pete]

In that case it would be fine for me with it mounted where you have it. 

 

@J.R. I doubt very much that there's a diode en route to your lighter socket, more likely inaccuracy of the LED meter. Verify against something less cheap.

 

[Mark-Surrey]

What’s the highest voltage a healthy Skoda battery would reach, when it’s fully charged? I’ve had my CTEK battery charger / conditioner hooked up to it this afternoon, and it’s currently showing 14.26V in the BM2 app on my phone.

[Breezy_Pete]

When was the charger disconnected?

No point looking at voltage within less than a couple of hours of disconnection.

[Mark-Surrey]

4 minutes ago, Breezy_Pete said:

When was the charger disconnected?

No point looking at voltage within less than a couple of hours of disconnection.

It’s still connected now. I charge it through the CTEK 12V socket adapter/dongle inside the car

[Breezy_Pete]

Thought so. Can't tell much remotely whilst charger is doing stuff. 

 

[JohnArm]

1 hour ago, Mark-Surrey said:

What’s the highest voltage a healthy Skoda battery would reach, when it’s fully charged? I’ve had my CTEK battery charger / conditioner hooked up to it this afternoon, and it’s currently showing 14.26V in the BM2 app on my phone.

Depends on the charger and if it has a float mode, I have one like these for my motorbike, and which ahs been used on other cars: https://www.ctek.com/uk/battery-chargers-12v-24v/vehicle-type/motorcycle/mxs-5-0-uk

 

At over 14v the manual for the above charger says it's either still charging, or coming down from the maximum: https://www.ctek.com/storage/5F698282EF11914E368ECD2BA726D2FC8F329CA0DA934C5E86A538F9AC089C23/00000000000000000000000000014050/pdf/media/b92f3bd538ed40b1bc345ee44e44d4fa/MXS_5.0-manual-low-UK-EN.pdf

 

I have a small LED voltmeter in the 12v socket and it can show almost 15v at times, though I do think that it overreads a bit. On my 2023 car it's a pity that the MySkoda app doesn't include the batteries voltage.

[Mark-Surrey]

2 hours ago, Breezy_Pete said:

Thought so. Can't tell much remotely whilst charger is doing stuff. 

 

I just unplugged the charger now. I noticed the voltage drop significantly, just after I unplugged it. It then started increasing again slowly. I’ll see what voltage it shows tomorrow morning. Without this BM2 device to see what’s happening to the voltage in real time, I would never have been able to see what actually happens when you use a battery charger

[BoxerBoy]

I tuck my motor bike away for the winter connected to an Optimate 4 charger.

 

8 years old and has fired up immediately every spring when it comes out of hibernation.

 

Should work for a car too.

 

Not that I’ve ever treated a car this way.

[Mark-Surrey]

I checked it this morning, and it’s now showing 12.62V. Is that the level where a 12V battery in reasonable condition should be?

[Breezy_Pete]

OK, yes, although EFB/AGM types tend to be a little higher than that, and than conventional batts when fully charged and unconnected to anything (open circuit).

 

Which is yours?

(It's likely to say EFB or AGM on the top).

 

Has it been giving any trouble?

 

Worth noting that the car's inbuilt charging system does not maintain 100% charge levels deliberately,  to avoid potential overcharge issues.

 

Edited 12 November, 2023 by Breezy_Pete

[Mark-Surrey]

24 minutes ago, Breezy_Pete said:

OK, yes, although EFB/AGM types tend to be a little higher than that, and than conventional batts when fully charged and unconnected to anything (open circuit).

 

Which is yours?

(It's likely to say EFB or AGM on the top).

 

Has it been giving any trouble?

 

Worth noting that the car's inbuilt charging system does not maintain 100% charge levels deliberately,  to avoid potential overcharge issues.

 

It says EFB on the battery.

 

It was almost completely discharged a couple of weeks ago, after using it only infrequently, and only for short trips. But I have recharged it since then with my CTEK MXS 5.0 battery charger/ conditioner. The Skoda breakdown assistance guy said that the almost complete discharge was likely to have reduced the future performance of the battery somewhat

[Mark-Surrey]

On my CTEK MXS 5.0 battery charger, there is a specific setting for recharging “AGM” batteries. But I have just been using the standard car battery setting. Should I be using the AGM setting for an EFB battery? I have no idea what these terms refer to!

[Breezy_Pete]

It's true that deep discharge is bad for car batteries. Sometimes they recover OK, sometimes not.

Your new monitoring device puts you in a great position to avoid any recurrence.  

Maybe set a reminder to check what it's saying once a week.

 

[Breezy_Pete]

Ask ctek if it's not in the user manual.

[Mark-Surrey]

1 hour ago, Breezy_Pete said:

Ask ctek if it's not in the user manual.

I just checked the CTEK user manual. Under the setting for “AGM” option, it doesn’t list any other types apart from AGM. So I’ll just stick with the standard  / normal profile for car batteries. But I noticed that there is also an option for “Recondition” mode, which it says should be used after deep discharge, to maximise lifetime and capacity, with a suggestion that this should be done once per year. I have never used this program, in the 3 years since I bought this CTEK charger. I’ll give it a try next weekend, to see whether it makes any difference.

 

 

[Breezy_Pete]

I don't think I would try that recondition function unless the battery is actually in a state of deep discharge, unless you get CTEK to say it is OK for an EFB that is near or at full charge.