Installing a 12 V battery monitor

[alohart]

A 12 V battery can fail without much warning. Installing a 12 V battery monitor could provide some advance notice of a failing battery. For those who have installed a 12 V battery monitor, I would like to ask for some installation advice.

I already have a 12 V battery charging harness attached to the 12 V battery under the tightening nuts of the 12 V positive and negative terminal clamps. This allows me to merely plug in my battery charger rather than having to feel around trying to attach a charging clamp to the positive terminal which can be challenging. As a result, there's really no room to install the battery monitor lead lugs under these clamp tightening nuts.

An alternative 12 V battery monitor installation location would be on the 12 V terminals under the rear cargo floor. However, removing these terminals so that the lugs of the battery monitor leads could be installed under the terminals requires a Torx bit larger than the T-40 that I have. What size Torx bit is needed? Of if you didn't loosen these rear terminals, how did you install the battery monitor leads?

 

[alohart]

I removed the 12 V rear positive terminal to determine whether I could insert the lug terminating the positive lead of the battery monitor beneath the terminal. Both rear terminals appear to require a T50 Torx driver which I and my local hardware store don't have. Instead, I used Vice-grips to loosen the positive terminal without doing much damage (ugh!). The design of the positive terminal precludes inserting a lug beneath it, so I gave up on installing my battery monitor in the rear under the cargo floor.

The positive battery terminal clamp has a threaded tightener long enough to accommodate a second 10 mm nut. I had already inserted the lug for my battery charger harness beneath the clamp tightening nut. By adding a second nut, I was able to insert the lug for the positive lead of the battery monitor between the first and second nuts and still close the red plastic protective cover over the terminal.

I was able to unscrew the negative terminal clamp tightening nut past where it was designed to be loosened. The threads on the end of the tightener have been buggered to prevent the nut from being removed and potentially dropped into oblivion. I had to unscrew the nut farther than normal so that I could insert both the battery monitor and charging harness negative lead lugs under the nut.

I tightened both terminal clamps, reconnected the HV disconnect, and determined that both the battery monitor and charging harness work normally. What should have been an easy job turned out to be a real pain in the butt because I was connecting 2 leads to each terminal and the terminals, especially the positive, aren't particularly accessible.

 

[3pete]

I removed the 12 V rear positive terminal to determine whether I could insert the lug terminating the positive lead of the battery monitor beneath the terminal. Both rear terminals appear to require a T50 Torx driver which I and my local hardware store don't have. Instead, I used Vice-grips to loosen the positive terminal without doing much damage (ugh!). The design of the positive terminal precludes inserting a lug beneath it, so I gave up on installing my battery monitor in the rear under the cargo floor.

The positive battery terminal clamp has a threaded tightener long enough to accommodate a second 10 mm nut. I had already inserted the lug for my battery charger harness beneath the clamp tightening nut. By adding a second nut, I was able to insert the lug for the positive lead of the battery monitor between the first and second nuts and still close the red plastic protective cover over the terminal.

I was able to unscrew the negative terminal clamp tightening nut past where it was designed to be loosened. The threads on the end of the tightener have been buggered to prevent the nut from being removed and potentially dropped into oblivion. I had to unscrew the nut farther than normal so that I could insert both the battery monitor and charging harness negative lead lugs under the nut.

I tightened both terminal clamps, reconnected the HV disconnect, and determined that both the battery monitor and charging harness work normally. What should have been an easy job turned out to be a real pain in the butt because I was connecting 2 leads to each terminal and the terminals, especially the positive, aren't particularly accessible.

Thanks for sharing. I'm coming up on 4 years with my car and have never replaced the battery (the PO allegedly did in the year they owned it) so I'm pondering if something like this would be useful for me.

A few questions if you don't mind/ know the answers:
1) what kind of monitor did you get? Bluetooth readout or one with an actual display?
2) any idea what the current draw of the monitor is? Would it have any negative impact on the battery life?
3) what's the typical reading while the DC-DC converter is off?
4) what threshold are you looking for from it to tell you to replace the 12v battery?

 

[EvanstonI3]

A few questions if you don't mind/ know the answers:
1) what kind of monitor did you get? Bluetooth readout or one with an actual display?
2) any idea what the current draw of the monitor is? Would it have any negative impact on the battery life?
3) what's the typical reading while the DC-DC converter is off?
4) what threshold are you looking for from it to tell you to replace the 12v battery?

1) I've had a BT monitor on my 2017 BEV since January of this year (2022) and it uses an app to read the monitor
2) Incredibly negligible like 0.01ma or something really insignificant if I recall
3) A fully charged, healthy battery will read 12.9-13.0vdc but will drop slightly over time. I've let my car sit for several days without use and it drops to maybe 12.7 vdc. The same battery, when fully charged and sitting on a bench not connected to anything, will read 13.0v for at least a week and will drop to 12.9 over a couple weeks. Takes maybe a month to self-discharge to 12.8vdc
4) The problem with that question is that once the 12v battery self-discharges to 12.0 volts, the DC-DC converter kicks in for One Hour to try and keep it "alive". What you are looking for is the 12v battery self-discharging rapidly over a short period of time.

Here is what mine looked like sitting for 24 hours and the DC-DC converter coming on periodically. The car does not have to be plugged in:

Note that the interval between "boost" charges is starting to get shorter as time progresses, until you get this: (or worse)

also note that BOTH these graphs are of a FAILING Battery. A normal one would just be a Flat Green Line that gently trends down a tiny bit. I'll post a pic of "normal" later.
Edit to add this is what a "normal" battery would look like sitting over the course of 1 day:

 

[alohart]

1) what kind of monitor did you get? Bluetooth readout or one with an actual display?

The first post in this thread includes a link to the monitor that I purchased. It connects to a smartphone via Bluetooth and uses a free app to display a time series of the 12 V system voltage for up to 30 days. Other functions like starter and charging tests aren't particularly useful for an EV.

2) any idea what the current draw of the monitor is? Would it have any negative impact on the battery life?

The documentation included with the monitor states that the current draw is 1.5 mA. A new i3 battery is rated at 20 Ah. Assuming that one wouldn't want to discharge the battery more than 50%, or 10,000 mAh, and that no other loads were discharging the battery, it would take 10,000 mAh /1.5 mA = 6,667 hours = 6,667 hours / 24 hours/day = 278 days for the monitor to discharge the battery 50%. Of course, there are other loads that consume considerably more current, so the battery would discharge 50% much quicker. My feeling is that an additional 1.5 mA load isn't a serious problem, maybe until the battery's capacity decreases considerably as it is failing.

3) what's the typical reading while the DC-DC converter is off?

That really depends on now frequently one drives and the age of the battery. I don't drive much, so the average charge level of our 12 V battery is probably lower than average, and thus the battery's voltage is lower than average. Curiously, the voltage of the 12 V battery on our 2014 was considerably lower than on our 2019 even though the battery in our 2014 lasted for over 7 years. The DC-DC converter almost always turned on when the HV system turned on unlike in our 2019. The "excessive discharging" message was occasionally displayed on our 2014, especially during the pandemic when I drove only ~100 miles/month. Fully charging the 12 V battery with a battery charger resulted in the warning message not being displayed again for several months.

On our 2019, the battery voltage immediately after the DC-DC converter turns off is ~12.9 V dropping to ~12.7 V after being parked for 24 hours with the burglar alarm on. The battery is probably the original which is ~3.5 years old in a car that's been driven a total of 32k miles.

4) what threshold are you looking for from it to tell you to replace the 12v battery?

Rather than a voltage threshold, I'll be looking for the behavior reported by Evanstoni3 where the voltage is dropping faster and faster. That would indicate a reduced capacity, but that isn't the only failure mode. I suppose a short-circuited cell would result in a lower voltage which would be something else to look for. I'm not sure how an increase in internal resistance would appear in the monitor's voltage time series. Maybe that would be displayed as a increased voltage drop when the HV system turns on but before the DC-DC converter turns on, so a longer negative voltage spike.

I think this monitor is a big improvement over the voltmeter that I've had in the dashboard auxiliary power port for several years. Having up to a 30 day time series recording the 12 V system voltage at all times is a big improvement at the cost of a slightly higher battery discharge rate.

 

[websterize]

1) I've had a BT monitor on my 2017 BEV since January of this year (2022) and it uses an app to read the monitor

Which monitor, please?

 

[3pete]

Here is what mine looked like sitting for 24 hours and the DC-DC converter coming on periodically.

Fantastic! Great information, and I do like a good graph... thanks!

The first post in this thread includes a link to the monitor that I purchased.

Thanks Art for both the info and confirming the link was actually the monitor you got. I wasn't sure if that hyperlink was generically added by the forum or not but good to know it has at least one preliminary recommendation.

 

[alohart]

Thanks Art for both the info and confirming the link was actually the monitor you got. I wasn't sure if that hyperlink was generically added by the forum or not but good to know it has at least one preliminary recommendation.

Oh, right, this site does add links of its own when some words are encountered.

I chose this monitor based on recommendations of others who had installed it. Amazon has several that appear to be identical but are being sold by different companies for different prices which is common for cheap Chinese electronics. Look for the monitor that's the lowest price, looks identical to the others, has the 30-day time series feature, and communicates with a smartphone via Bluetooth.

 

[EvanstonI3]

1) I've had a BT monitor on my 2017 BEV since January of this year (2022) and it uses an app to read the monitor

Which monitor, please?

https://www.amazon.com/gp/product/B07WCW49YM/ is the BT Monitor I purchased. Don't know if it is the "best" but it works well for me.
They will want you to download an app called ANCEL MONITOR and it works OK but I discovered it is clone of another app: BATTERY MONITOR. The main difference seems to be that BATTERY MONITOR gives you options for displaying the graph in 1Day/7Day/15Day settings while the ANCEL one is only 1Day.

 

[alohart]

https://www.amazon.com/gp/product/B07WCW49YM/ is the BT Monitor I purchased. Don't know if it is the "best" but it works well for me.
They will want you to download an app called ANCEL MONITOR and it works OK but I discovered it is clone of another app: BATTERY MONITOR. The main difference seems to be that BATTERY MONITOR gives you options for displaying the graph in 1Day/7Day/15Day settings while the ANCEL one is only 1Day.

I learned that the "ANCEL Battery Monitor" app also works with the less expensive Battery Monitor BM2 that I purchased. However, as you wrote, it doesn't offer the choice of time series periods which is important to me, so I deleted it. I also installed the "BM500" and "Battery Sense" apps, but neither would pair with my battery monitor, so I deleted them as well. I'll stick with the "Battery Monitor BM2" app that is slightly superior to the "ANCEL Battery Monitor" app and good enough for my needs.