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Battery Monitor hooks up easily and provides useful info

1116 Views 13 Replies 9 Participants Last post by  Trielectric
After reading this comprehensive post on battery monitoring, I finally broke down and got two monitors, one for each 12v battery. (Note that 2021 and later models have only one battery.)

Here’s the BM6 monitor I bought. You can see it here on Amazon. It's deceivingly can fit two in the palm of your hand.
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Download the required app by using the QR code on the monitor or looking for it where you get your apps.

Hooking it up and setting up the app were simple, and the (Android) phone read the battery monitors automatically, without going through the normal Bluetooth pairing process. In fact, even when the monitors are connected to the phone, you cannot see the monitors on the phone’s list of Bluetooth-connected devices.

Connecting the monitors to the phone requires that you enter the monitors' serial number in the app. Take a photo of this number so you have it handy, since once the monitor is installed, you may not be able to see the number easily. I’d recommend hooking up one monitor and make sure everything is working before hooking up the second monitor and battery. To add the second monitor for the Aux battery, I just entered the monitor’s serial number and it, too, began reading instantly.

Here’s what the app’s home screen looks like. It gives the battery's SOC as well as the voltage and temperature, and can monitor four batteries. When it's charging, the app will say "Charging" where it says "Battery OK".
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And here’s a sample app-generated graph showing both batteries’ voltage. You can also display SOC or temperature, and it will also export the data using Excel.
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The export feature allows you to export the data from either 12v battery, but the Excel spreadsheet it creates is awkward. The interface exports tabs within the cells, so they don’t work for charting. You’ll have to do some manipulating to get rid of the tabs and leave a number in the cell before creating a chart. You’ll also need to reformat the dates if you’re going to use Excel. In the end, I found it easier to just use the charts that the app creates.

The Android app is a real battery hog for your phone, and it won’t let the phone sleep while you have it displayed. Shut it down when you’re not using it…the data will catch up next time you start the app within range of the car. The monitors will store 32 days of data that the app will collect next time it's connected.

The app is intrusive, and wants permission for all kinds of access to the phone…some of which you may not want. My advice would be to grant everything it asks for until you have the app and monitors running to your satisfaction, and then change the access later if you want to.

FYI, the BM6 app will NOT connect to the monitors without the phone's location enabled, even if you’re not using any location-required features.

Now that it’s installed, it works great… but I’ve got some issues with the readings I’m getting. I’ll put them in another post.
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I got a single victron module to test out. It comes from an ecosystem of devices, and comes from a company that I feel less paranoid about installing software from. The only permission is to detect nearby devices, which makes total sense since... it has to detect nearby devices. I hooked it up to my generator's 12v battery, and will get a few more for the EVs so I can monitor all of them.
You can also find the same BM6 at AliExpress, e.g.:

I also yielded to the temptation of getting one after reading the same post, but I'm testing it on a Diesel car - it was easier to get at the battery.

The software does not look too solid - connections to the phone seem hit and miss, and perhaps because of that, the location/trip-recording doesn't seem to work as it should (I believe I supplied the required permissions).

The battery data itself seems OK, I compared it to another reading at a 12-V socket and it matched close enough.
Yes, I checked mine against a digital voltmeter, and they were the same.

The car however, reads higher. When the monitor says, for example, that the voltage is 13v, the car (via WattCat) reports around 14v.
I have used very early model bluetooth battery monitors using early version BM series apps. Yes they are android phone battery hogs, the app will not show any battery voltages until it obtains your GPS permission & position as the app wants to track your journeys ( spyware?) . If you don't gave permission the app wont run. Yes you need to manually force Stop to stop the heavy phone battery drain.

I find the best way to extract useful data using the BM apps to download say the last week or so data and then force stop the app. The module devices will store approx 30 days of data

The battery SOC charts do not seem to be of any use unless you can inform the app of each battery's particular characteristics ie AGM has a much higher resting Voltage than a gell cell, wet cell or flooded batteries. I cannot recall if this setting is possible.

It is also important when monitoring the larger Start battery that the monitor module -ve terminal must go to a proper body earth terminal and not the actual battery -ve terminal as this part of the cars monitoring system.

Cheers, Steve
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They've made a few improvements to the latest version of the BM6 app. One is that you can define the battery type, so that the app takes battery type into account when calculating SOC.

Another is that the app does not continue to run in the background if you close it. (But if you leave it open, it still won't allow the screen to shut off to save power.)

Good advice on connecting the monitor's negative lead... I'll make that change.
You need to connect the monitor to the negative post as shown in my original post. On the startup battery, it connects between the posts so as to bypass the BMS that is electrically between the body and the negative post.

The BM2 monitors I installed have the option of setting the battery type as "Regular 12V lead-acid battery", "AGM battery" or "Custom battery". Custom opens up another menu of options for power algorithm and "power and voltage correspondence table".
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I used these monitors to convince my dealer that there was a problem with my DC-DC converter. I printed out a chart showing that the battery wasn't charging when it was supposed to and they were finally able to diagnose the problem after having made multiple visits to the dealer.
After a few weeks of watching the batteries charge and discharge, I'm not seeing anything alarming. Although I'm not sure where these voltages should be. (There have been no additional car problems during this time.)

The Start battery bottoms out at 12.67v. This sounds normal to me. After charging, it reaches this level within 24 hours.

The Aux battery bottoms out at 12.77v. From a full charge, it takes about 24 hours or so to reach that low point, and seems to level off there. I believe 12.8v to 13.0v is normal for an AGM, so this is pretty close.

And use caution if you're using WattCat to monitor your Aux battery levels. WattCat is reporting 15.0v at this time, while my battery monitor is reporting 13.0. My digital voltmeter also reads 13.0. WattCat sometimes agrees, but more often, it's at least 1v higher than the monitors.

I wonder if that could be a problem... when the car believes the Aux battery voltage is higher than it really is.
Hopefully the car dies not rely on WattCat to operate it !
The dealer checked my batteries, and both failed when tested. They replaced both under warranty.

The new batteries are steady at 12.85v and 13.02v respectively, 24 hours after charging. Both SOCs read 100%, for what it's worth. (The old batteries were at 12.67v and 12.77v respectively).
From my experience you will not learn anything from battery monitoring until your car will not go. A voltmeter would be helpful at that point to confirm it is the 12v batteries. In the old days you might notice your ICE was not cranking(superhigh load when cranking) as fast as it usually did and you would go and get a new battery. We don't have that kind of load on our 12v batteries to give us a heads up of a failure approaching.
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I had battery monitors for about 8 months. When I first put them on I was seeing 13.0/12.8 volts AGM/FLA after sitting 24 hours. Then I noticed the FLA would be at 12.5 volts after 24 hours a few months later. Then 12.0 volts a few more months later. I preemptively changed the FLA and now I am at 12.8 volts after sitting for 24 hours again. I chose to pay/do it myself instead of wasting time with the dealer. I’d like to think I avoided being stranded.
With a temp battery in the car suggestion, that I got on this site, I was never stranded when my 12 volt batteries failed.
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