ANCEL BM300 12V Battery Monitor, Bluetooth 4.0 Automotive Voltmeter with Charging, Cranking System Test & Alarm - Compatible for Solar Power Systems, RVs, Motorcycles, Boats, Cars, and Trucks

Very easy to install, instruction easy and products seems well built. I like the APP feature took less than 5 minutes to download and setup

Works great

New EVs seem to have intermittent issues with their 12V batteries, such as not being charged properly or failing and causing the car to respond erratically, sometimes even while driving. After replacing the stock 12V battery in my new EV because it was not able to hold a decent charge unless it was constantly being charged, I wanted to ensure that my new battery was working, and that the car's charging system was working to charge the 12V battery. The BM300 allowed me to do this. It is a small device that can be attached to the battery hold-down clamp and transmits using low-energy bluetooth signals to your phone running their app. The app displays the voltage and state of charge. It also logs the voltage history over time, which is very useful for seeing how your battery is discharging and then recharging. The product does a good job at this and seems to work well with the app. Sometimes it takes a bit longer than others to connect to the app, but it usually does connect properly.About the only issue I have experienced with the app is how it interprets the voltage. The device does appear to accurately detect the battery voltage since it matches my multimeter when I test it myself. However, the app attempts to interpret the state of charge and display it as a percentage, also indicating if the battery is "ok" or "low" depending on this interpretation. You can also set alerts based on the state of charge if desired. The issue I experienced on two of these devices was that it would show a voltage of something like 12.5V and indicate that the battery was 90% charged. Another device on the other car's battery would show a similar voltage like 12.45V, but the percentage would be displayed as something like 65%. I have deleted the device and reinstalled it in the app and made sure the batteries were both set to AGM type (because they are), but the app seems to intermittently interpret the same voltage with wildly different percentages. Ultimately, this doesn't really matter as the state of charge percentage is really just for easily understanding your battery's state. The voltage appears to be consistently accurate and that's all that matters, especially if you know what your battery's voltage range should be.I was also able to confirm my car was recharging the battery properly while being charged as I could watch the battery voltage rise to the proper level during charging. This was reassuring as I was able to test more than just the battery using this device.So ultimately, it does work and the feature of logging the historical charge voltages over time is very helpful. If the state of charge interpretation was more consistent (it is correct some times), then it would get a full 5 stars. Customer service from the seller has been responsive and truly appears to be interested in resolving any issues. I just haven't been able to get that one feature to work consistently. However, I would still recommend this as it seems well made and does a good accurate job at recording the battery voltage, which is ultimately what counts.

I've got one of these on each of my trucks. It works great and allows me to see what is happening with the 12V battery while the truck is off.Today's vehicles have many modules and some don't shut off until a half hour after the ignition is switched off. Some manufacturers are installing 12v batteries that are too small for all of the conditions the vehicle may face - such as vehicles parked outside during very cold winter temps. If the 12v gets too low it can cause all sorts of warnings and problems in your car. Knowing your battery voltage over time is extremely helpful in diagnosing battery issues.

Pictures starts with normal idle voltage, then 20min drive then on a low current charger, 1.5amp, then the phases of the charger to trickle charge then off the charger with a 20min drive. Next picture is the start screen, each vehicle has a different signature of the 3 I've installed currently. (Screen shot the typical starting signature for referencing later if issues arise.) Sometimes it takes a minute or two for the phone to find the device even if it's the only one in range. There seems to be an issue with more than one phone trying to use the same device at the same time. Sometimes it will just switch to another device if 2 are near by. You can view data by selecting the device after it's done scanning in the GEAR-> BLUETOOTH DEVICE-> SELECT DEVICE then tap the arrow/carrot to the right of the listed devices. Having a few months worth of data is very helpful. If you tap the center of the calendar day at the top of the screen you get a calendar with blue dots for data for that day or a red dot for data that was outside the normal ranges. No more guessing or relying on unclear observations or faded/shaded memories of other people!