Battery maintainer install directly to 12V battery

My practice is identical to that of @Xse, and I can't see that there has been any harm to the trunk lid or its gasket.

 

I just finished getting a live 12V socket installed (with a switch and a circuit breaker). This will enable me, among other things to gauge the 12V battery voltage level before I start the car. I'm using a volt meter that plugs into a socket, but unfortunately it didn't show battery voltage until I had already started the car. Now I can switch it on while the car is off. I had suspected that the lower limit for the voltage to start the car was somewhere below 11.5 volts. Now I will be able to know for sure

 

You're right to want to see what the battery is doing when the car is off, but once you get into the car, it isn't completely off. That's why I rigged my minimal voltmeter (MINI VOLTAGE DISPLAY, 2.5V-30VDC, 2 WIRE CONNECTION) to be permanently connected, and visible near the right rear passenger shoulder strap from outside the car. That lets me sneak up on the car and see what it is up to when it is truly off.

 

I've got a bag of those panel meters. I even 3D printed an enclosure for it.
Using one was my first thought, but this switchable live socket is a bit more useful.

 

Have you ever seen this?
I have BM2s on both of my cars and occasionally I've see what I hope is a software glitch (it's happened on both BM2s).
I see a voltage spike on the graph of exactly 39.25V. So far it's happened 3 times over the length of about a week.
2 times a NoCo2 was attached and one time none were attached.
Thoughts?
J

 

I doubt that such a voltage spike of very short duration is harmful to the battery. It may be part of a testing cycle designed to detect sulfation.

 

If I want to check voltage without waking up the car, I use a tip from @bisco: pop the hood the night before, then check with a volt meter, first thing in the morning. In my case I've got a quick-connect for a charger permanently wired in the engine bay, so I use that, but the jump point in the fuse box would serve as well.

If I don't have the hood popped, I at least wake up the car "less", by entering via passenger door, reaching across, to pop the hood.

 

If I pop the hood I get an animated warning on the MID that stays on until I close the hood. I have to believe that uses power. I haven’t found a way to disable the warning.

 

I like my way. I had a live socket installed under the dash. I have a plug-in volt meter/digital thermometer plugged in. I can check my battery voltage at a glance from outside the car, and get the interior temp as well.
The socket is through a switch, but the drain is so small, I can leave it on for several days at least.

 

That is a software glitch, not a real reading. A real value would also show on the voltage curve.

BM2 samples and records the voltage every two minutes. It does not record instantaneous voltage spikes. If 39.25 were real, it would fry your car electronics and possibly damage the battery as well.

 

BM2 is far better, more practical, more informative, and more useful than manually hooking up a voltmeter, as it records the voltage every two minutes for the last several months. It is also far more accurate than a cheap voltmeter, which could be useless, as the latter won’t have the necessary 0.01-V accuracy to fully diagnose a lead–acid battery. The BM2 I have got is 100% accurate to 0.01 V against a calibrated voltmeter.

A digital air compressor is also far more useful than a bicycle pump. These modern devices are very cheap on Amazon; so, I don’t know why you object to them. LOL

 

After enlarging the picture, I see that there was an actual spike.

I am guessing that the actual voltage at that spike was a little larger than the 15.0-V maximum range on the y-axis, which is what caused the software glitch. Were you using the repair mode or regular mode? The repair mode does “current conditioning,” up to 16.5 V. Therefore, that spike would be 16.5 V or less in that case. Which amperage Noco Genius is that? The voltage could increase with the amperage, but it won’t exceed 16.5 V. You should disconnect the negative cable of the battery if you are using the repair mode.

 

No repair mode.
There were 3 occurances and on at least one of them no Noco Genius was attached so I'm ruling that out.
I was worried if the 39volts was real how much of the Prius electronics could be at risk to be damaged. So far, all seems OK.

On an aside there are 2 versions of the BM2 software available for iOS. When I had my first BM2 installed (by my dealer at time of delivery of my Gen5/Non-Prime) I was using the Free single monitor version. After I added the second BM2 (also installed by my dealer when I replaced the battery on my wife's '21 Venza when it's battery failed in -12°F weather I purchased the 4 unit BM2 software. Both versions showed the anomolies so if it's a software bug that bug exists on both software versions.

J

 

I have never seen the DC–DC converter producing voltages higher than 14.5 V in my Gen 4 Prius Prime.

Do you connect and disconnect inductive accessories like USB phone chargers, which are switching power supplies? They would certainly produce a voltage spike (as in a spark) when you disconnect them because the voltage across an inductor is proportional to the time derivative of the current through it, meaning a sudden current cutoff results in huge voltage spike.

 

No I do not have any such devices.
All occurances the cars were unoccupied. 1 in the garage the other on the driveway.
Not related (or is it?) but shortly after I notices the spikes one of my BM2s stopped connecting via Bluetooth.
Both BM2 graphs had spikes but only one BM2 failed.
I have no idea why. I wanted to disconnect one end from the battery to restart the BM2 but I had no metric sockets.
So I just purchased an inexpensive ratchet/socket (46 pcs) along with a new BM2 and I said screw it and just replaced it.
I probably should have disconnected/reconnected it but I was frustrated at the time.
As if this writing I have not experienced any more anomolies. Fingers crossed.
J

 

Perhaps it is a loose connection on the BM2 terminals then, with the BM2 momentarily losing power and producing a spike/spark. In any case, it doesn’t seem to be a cause of concern. Such spikes (causing sparks) also happen when you disconnect/reconnect the battery, but they will not have enough energy to damage the electronics.