Voltmeter for vehicle battery to monitor inside of cab

[BillyO]

Our tech support at headquarters (Bosch) does admit that the original battery in a car is often/almost always lower quality then after market.

Lots of issues with agm type batteries.

I wouldn't say Yuasa batteries are low quality.  Probably one of the best batteries worldwide.  IIRC, the Interstate (renowned for quality too, at least in NA) was about $175 less than the Yuasa at the time.  Something like $450 vs $275.

Edit: It's also interesting to note that my Austrian KTM motorcycle came with a Yuasa battery too, rather than a Bosch.

[Sorama]

Those brands are unknown to me, probably true for Europe in general.

[radiolistener]

Being in a minority generally means being wrong.

Just like the crazy ones think they’re right.

Yes, that may be true in some rare cases, but not as a rule. History offers countless examples where the minority view initially dismissed or ridiculed turned out to be correct. Scientific and technological progress is usually driven by those who challenge the consensus and think differently.

What is important is that simply being in the minority doesn’t make someone right, but it certainly doesn’t make them wrong either. What ultimately matters is the strength of the evidence, not how many people agree.

The truth isn’t determined by the number of voices behind it, it’s determined by logic, facts, and evidence.

To me, the majority opinion usually reflects the views of the most stupid segment within crowd (this can be easily approved statistically). Arguments based solely on majority agreement come across as if you’re saying "I’m right because my opinion matches that of the most stupid peoples in the crowd". This doesn’t necessarily mean that such an opinion is always incorrect, no it just reflects the perspective of the most stupid segment of the crowd. The reasons behind such opinions among can vary - they may stem from manipulation or simply from ignorance, etc. Regardless, the essence remains the same - it represents the opinion of the most stupid peoples of the group.

What I’m genuinely curious about is why the opinion of the most stupid peoples of the crowd holds such a high priority for you? 

[Analog Kid]

That's a rather iffy proposition, at best: that the majority view constitutes the stupidest one, the opinion of the great unwashed masses. Because why?

Just as iffy as saying that the majority view must be the correct one because, hey, most everyone agrees with it.

Just accept that in this particular instance, you're the outlier.

(We still need to hear from the OP on this. How accurate is accurate enough for you?)

[radiolistener]

Our tech support at headquarters (Bosch) does admit that the original battery in a car is often/almost always lower quality then after market.

That's interesting - in my experience, the original battery that came with my Toyota actually seemed more robust than any aftermarket one I've had since. It survived 4-5 full discharges within 4 years and still performed reliably. I eventually gave it to a friend, assuming it was near the end of its life, but it kept working flawlessly for several more years. In total, it lasted around six or even more years, which is better than most replacements I’ve tried.

My current battery is a Bosch, now about five years old. However, due to the war it is sitting unused most of the time. It's still functional, but based on the voltage behavior, it’s showing signs of aging - it used to hold 12.7 V for a long time, but now it drops to around 12.5 V relatively quickly and stabilizes there.

Overall, my impression of the Bosch battery hasn’t been particularly positive. It has always felt somewhat weak, and throughout its use I’ve had the sense that it was on the verge of failing - yet, somehow, it has managed to last five years and still working, recently we had 24 hours power outage and it helped me a lot, because I forgot to charge my power banks.

[BillyO]

Well, if you take every man, woman and child in the US (not including illegal immigrants) into account, then only 18% of those actually did the totally stupid thing of voting in the deranged orange dung pile.  While that in itself does not disprove that the majority are stupid, it is a data point of evidence to that point.

[radiolistener]

I would argue that the issue is not who people voted for, but the very act of voting itself. Regardless of the candidate chosen, anyone who participates in the electoral process implicitly accepts and legitimizes the authority imposed by the system, effectively consenting to be governed by whoever wins, regardless of their qualifications, character, or how they came to power, honestly or not. This is real indicator of stupidity.

The critical point is that by voting, individuals voluntarily submit to a structure of imposed power rather than questioning or challenging the legitimacy of that authority. And moreover, the fact that the majority still participate in elections suggests, in my view, proof that most people are stupid and lack critical awareness and are therefore, easily led - effectively endorsing a system where they are assigned the role of subjects or "servants" to the ruling class.

Even the act of casting a ballot holds symbolic significance: by placing their vote into the ballot box, individuals symbolically consign their opinion to the trash bin, implicitly acknowledging its disposability and futility.

However, to recognize that the majority of people are stupid, it is not necessary to invoke politics - mathematics alone suffices. In any sufficiently large sample, intelligent individuals will constitute a minority, while the stupid will form the majority. No matter how large the sample, you will observe a normal distribution, with relatively few highly smart people and a predominance of stupid. Consequently, the prevailing opinion within such a group tends to reflect the views of the stupid majority rather than smart minority.

And you cannot change this, because this is a fundamental mathematical characteristic of our world.

[BillyO]

effectively consenting to be governed by whoever wins

I imagine some of your reply has been borrowed, but this statement in particular would need some serious justification.  History provides us ample evidence that this is not the case.  Revolution is and always will be an option that effectively nullifies your assertion.

However, as interesting as a deep discussion regarding the philosophy of democracy is, it represents a considerable drift in the subject of this thread.

I apologize for starting this.  I'll give you the last word on this "side-track".  Perhaps "derailment" might be a more apropos term.

[UnijunctionTransistor]

This particular model will display two decimals below 10.0 volts, but even a single decimal is enough for general purpose battery monitoring.

Your photo shows 12.0 V, which is quite low and potentially concerning. If the engine is off and there's no charging, this voltage indicates a low state of charge - roughly around 30%. A healthy, fully charged battery should read about 12.7 V at rest (no load, no charging).

After charging, the battery may retain higher voltage for some time (due to internal chemical processes), which gradually stabilizes to its true open-circuit voltage 12.7 V over the course of approximately 30-40 hours.

If the engine is running and charging is active, you should typically see 13.0 to 14.4 V, depending on the vehicle and temperature.

The engine wasn’t running, and the car had been parked for a couple of days. Additionally, I had to readjust the power seat because my wife had previously driven it and she is significantly shorter than I am.
When the engine is running, it jumps to 14.1 V.
And to maintain my sanity, every now and then I open the bonnet and measure the voltage across the battery terminals.

My primary reason for adding this meter is precisely to determine how much the voltage is depleted when the vehicle is parked. We travel a lot, and is not uncommon to be away from home 10 to 15 days.

[Analog Kid]

I would argue that the issue is not who people voted for, but the very act of voting itself. Regardless of the candidate chosen, anyone who participates in the electoral process implicitly accepts and legitimizes the authority imposed by the system, effectively consenting to be governed by whoever wins, regardless of their qualifications, character, or how they came to power, honestly or not. This is real indicator of stupidity.

So you're saying essentially that voters are stupid.

I'd say it's looking more and more like you are the stupid one here.

[radiolistener]

So you're saying essentially that voters are stupid.

Yes, I do consider the act of voting - particularly without a deeper understanding of what is being legitimized - to be a sign of very stupid people. A thoughtful and critically minded person is unlikely to endorse a system that grants power over their life to someone they don’t even know personally, based purely on campaign slogans or media representation.


Imagine a scenario where 10 wolves and 3 sheep are sitting at a table, voting on what's for dinner. The wolves participation is understandable - they know exactly what they’re doing and are acting in their own interest.

But what about the sheep? Can we consider a sheep smart for simply taking a seat at that table and participating in such a vote? Or does the very act of joining that process raise serious questions about its stupidity?

[Analog Kid]

I think you just painted yourself into a corner there, pal.
Be careful where you track those footprints as you steal your way out of there ...

[radiolistener]

You mentioned I’ve "painted myself into a corner" but I’m genuinely curious - what exactly do you see as the corner, and why would I need to get out of it?

From my point of view, it's entirely rational to point out how flawed it is to participate in a process where the outcome is designed to serve interests other than your own. In a system where the act of voting serves primarily to legitimize authority - regardless of who wins, the voter effectively consents to be governed by whoever is chosen. Whether the winning candidate is the one you supported or not becomes irrelevant, because by voting, you’ve already accepted the rules of the game and agreed to the result in advance.

In that sense, participation itself is the trap - the real corner and the wisest choice is to avoid stepping into it in the first place.

In this context, the sheep demonstrates its lack of judgment simply by agreeing to participate in the process. The specific choice it makes - regarding who should be eaten for breakfast - is entirely irrelevant, because the outcome of such a game is predetermined from the start. What the wolves needed was not the sheep's vote, but its participation - to ensure that it would voluntarily accept the result. As for who the sheep actually voted for, the wolves couldn’t care less.

We seem to have strayed quite far from the original topic. It appears your goal is to catch me in some flaw in my reasoning. However, the issue is not that I invented these ideas,  I am merely paraphrasing thoughts articulated by renowned philosophers of antiquity.

In fact, by attempting to prove that the minority is always wrong, you fall into a trap yourself - appealing to the majority opinion as an authority. Logic is not determined by the number of opinions supporting it but is founded on sound reasoning. The quantity of people endorsing a particular idea is irrelevant, what truly matters is the validity of the logic, which remains constant regardless of how many individuals support or reject it. It seems obvious to me, doesn't it?

[Analog Kid]

You mentioned I’ve "painted myself into a corner" but I’m genuinely curious - what exactly do you see as the corner, and why would I need to get out of it?

You just don't get it, do you?
Like my dear departed dad used to say (too often) to me: "Quit while you're ahead".

[BillyO]

"Quit while you're ahead".

Is he ahead?

[Analog Kid]

"Quit while you're ahead".

Is he ahead?

Nope, and that's the irony of it.

[CatalinaWOW]

You mentioned I’ve "painted myself into a corner" but I’m genuinely curious - what exactly do you see as the corner, and why would I need to get out of it?

From my point of view, it's entirely rational to point out how flawed it is to participate in a process where the outcome is designed to serve interests other than your own. In a system where the act of voting serves primarily to legitimize authority - regardless of who wins, the voter effectively consents to be governed by whoever is chosen. Whether the winning candidate is the one you supported or not becomes irrelevant, because by voting, you’ve already accepted the rules of the game and agreed to the result in advance.

In that sense, participation itself is the trap - the real corner and the wisest choice is to avoid stepping into it in the first place.

In this context, the sheep demonstrates its lack of judgment simply by agreeing to participate in the process. The specific choice it makes - regarding who should be eaten for breakfast - is entirely irrelevant, because the outcome of such a game is predetermined from the start. What the wolves needed was not the sheep's vote, but its participation - to ensure that it would voluntarily accept the result. As for who the sheep actually voted for, the wolves couldn’t care less.

I will point out that since quite a bit less than half of the eligible voters did vote either way, by your logic Americans are by and large smart.   I find that a foolish conclusion and disagree with your other observations.

But I really read through the through the thread (very rapidly) interested in the OPs question and find that everyone's comments are directed towards the OP's assumption that there might be a battery problem.

My own reaction to the situation is that given sufficient understanding the OP might get a better understanding of his system electrical problem with a voltmeter at the cigarette lighter or any other convenient point.  Three digit accuracy should be plenty, and the goal should not be limited to attempting to assess the battery state of charge, but what, if any problems exist in the system.  It could be something faulty with the idiot light.

For example, bad connections at the battery terminal will cause voltage drops throughout the system under load.  A bad enough connection will result in a low voltage engine off due to whatever small loads exist, but the voltage will rise unrealistically fast when the engine starts and the alternator kicks in (in many, perhaps most cases the maximum alternator current won't drive the battery internal impedance hard enough to bring a severely low battery up to full charging voltage immediately).  Another situation I have run into repeatedly is that there are multiple taps off the positive battery terminal.  Sometimes there is high contact resistance in some of the taps, and not others.  The OPs idiot light might be attached to such a tap.  Finding an appropriate voltage at the cigarette lighter or other test point could give a false sense of security, since there might be something more important than the idiot light on the same circuit. 

Diagnosing all of the possibilities requires quite a bit of understanding of the electrical system of the specific vehicle, and at least a rudimentary understanding of ohms law and how much current flows in each of the circuits.  This may or may not be in the OP's wheel house. 

[radiolistener]

I will point out that since quite a bit less than half of the eligible voters did vote either way, by your logic Americans are by and large smart.   I find that a foolish conclusion and disagree with your other observations.

I’m not deeply familiar with the specifics of the American electoral system and don’t wish to delve into it. I view all these systems largely as a spectacle, where the core purpose is the act of participation itself - to legitimize the outcome.

Consider loyalty programs in large retail chains. Customers are encouraged to join and actively participate by collecting points and redeeming rewards. The core purpose isn’t necessarily to offer genuine value to each individual, but to create the appearance of engagement and loyalty. The act of participation itself legitimizes the program and keeps customers invested, even though the actual benefits may be minimal or structured to primarily serve the retailer’s interests.

For example, bad connections at the battery terminal will cause voltage drops throughout the system under load.  A bad enough connection will result in a low voltage engine off due to whatever small loads exist, but the voltage will rise unrealistically fast when the engine starts and the alternator kicks in (in many, perhaps most cases the maximum alternator current won't drive the battery internal impedance hard enough to bring a severely low battery up to full charging voltage immediately).  Another situation I have run into repeatedly is that there are multiple taps off the positive battery terminal.  Sometimes there is high contact resistance in some of the taps, and not others.  The OPs idiot light might be attached to such a tap.  Finding an appropriate voltage at the cigarette lighter or other test point could give a false sense of security, since there might be something more important than the idiot light on the same circuit. 

Diagnosing all of the possibilities requires quite a bit of understanding of the electrical system of the specific vehicle, and at least a rudimentary understanding of ohms law and how much current flows in each of the circuits.  This may or may not be in the OP's wheel house.

Exactly, that is precisely the point I have been making - to properly test a battery, measurements must be taken directly at the terminals. This approach allows us to verify the battery’s condition in one step, if the battery is ok, we can then proceed to examine the wiring. Otherwise, measuring voltage at the cigarette lighter or elsewhere does not provide certainty about whether the battery or the wiring is functioning correctly. In other words, such measurements lack a reliable reference point to determine what is truly operational and what is not.

[Simon]

How did we end up at politics over fitting a battery voltmeter?

[electroniclearner820327]

Selected one of the many digital voltmeters available online, trimmed the lead wire to proper length, attached a cigarette-lighter plug, double sticky tape, and in less than 15 minutes you are good to go.

This particular model will display two decimals below 10.0 volts, but even a single decimal is enough for general purpose battery monitoring.

I am not understanding all these suggestions to plug it in anywhere. As is mentioned by some others, how will that tell me the voltage of the battery if it isn't connected directly?

I don't see how if it is only plugged into the lighter terminal that it could tell me the overall voltage of the battery? Is the idea that the whole system uses the battery and so it will show the voltage wherever you have a circuit to it?

I agree that it doesn't have to be super accurate but I also want to see the voltage increases when it should be charging with the alternator. Does the voltage rise and fall even for the other appliances in the starter batteries' system?

I am most familiar with leisure battery/lifepo4 electrics. I had never really thought about it though if the voltage is rising and falling for all things connected when the solar is rising it through charging, for example. Is that the case?

Another thing I did think of though, is that if connecting to the wire the dc-dc charger also uses then wouldn't that blow the voltmeter as there are high amps going through that or would it only draw as much as it required, with a low amp fuse on that line of course? If there will be 40+ amps flowing through that circuit on the main battery wires when the dc-dc charger is running is there still a way to have the voltmeter connected and not have it blow as this would be very convenient to wire it to this existing circuit?

There seem to be two issues which are being conflated so far:

-where it should be connected to power the device.
-where it should be connected to give accurate voltage readings for the starter battery.

I mentioned connecting it between the starter battery and dc-dc charger circuit because that is connected directly to the battery and also the wire runs between the engine compartment and into the van.

[electroniclearner820327]

without knowing a lot more detail about the exact wiring it's hard to advise you on this.

See this previous thread where there is a wiring diagram. One by myself in the attachment of the OP and also an amended one by another user later on as apparently my original one was hard to understand and not formatted in the usual way, which I am not familiar with.

[electroniclearner820327]

The idea is to know  whether the battery is being charged or not.

You do t need a 6.5 digit meter for that nor any exact battery voltage as any 12V power line will tell you if there is a problem or not.

You're right that any significant voltage drop typically indicates a problem - but only if you're measuring at the correct point. That’s exactly why connecting a voltmeter anywhere other than directly at the battery terminals can be misleading.

In a vehicle, wires and connections are exposed to vibration, moisture, corrosion, and mechanical wear. A wire might be partially damaged, corroded, or have a poor contact, which can create resistance. As a result, the voltage at some 12V line inside the vehicle might appear low - making it seem like the battery is undercharged - even if the battery is actually in perfect condition. Or worse, it might appear normal while the battery is failing, simply because you're measuring after a faulty connection.

If your goal is to know whether the battery itself is being charged, and what its voltage is under various conditions, then the only reliable method is to measure voltage at the battery terminals. This eliminates the influence of unknown or degrading vehicle wiring and ensures you're seeing the true battery status - not what’s happening downstream at, say, the cigarette lighter or a fuse panel.

In short: if you want to monitor the battery, measure at the battery. Anything else may tell you more about the wiring than the battery itself.

But even a voltmeter will not tell you if there is enough charge in the battery.

a voltmeter alone won’t give you the full picture of battery health unless it's connected directly to the battery terminals and used properly.

When voltage is measured at the battery terminals, you can absolutely assess both the state of charge and get a good indication of the battery’s condition. Measurements taken elsewhere in the vehicle’s wiring, such as at a cigarette lighter or accessory circuit - are affected by wire resistance, voltage drops, and potential faults. These measurements not only fail to represent the actual battery voltage but can’t reliably indicate battery condition at all.

To evaluate state of charge, just let the battery rest for 30-40 hours at ~25°C without any load or charging. Then measure the open-circuit voltage directly at the battery terminals. This gives you the battery’s EMF. Then you can estimate the charge level in percents with this simple approximation:

State of charge (%) = (Voltage - 11.7) * 100

To assess internal resistance, again connect the voltmeter directly to the terminals. Measure the voltage with no load, then under a significant load (e.g., headlights + heater).

Even without measuring current, a large voltage drop under load indicates high internal resistance - a sign of battery aging or failure.

But notice very important thing - in all cases, reliable conclusions require voltage measurement directly at the battery terminals. Anything else may mislead you due to unknown wiring losses or faults.

This reply goes in to great detail as to my confusion mentioned in post above as to why many are recommending to just plug it in anywhere. You explained it far better than I could have. It doesn't have to be pinpoint accurate but it certainly has to be taking its readings from the right place!

[electroniclearner820327]

electroniclearner820327, intermittent battery light is on the vehicle's instrument cluster, but not sure what a "cab" means in the UK. What vehicle is this? Here a cab=taxicab. Some semi trucks (24V) have a cab though.

It just means being able to monitor inside the dashboard/cockpit of the vehicle. Cab = where you are sitting when driving.

The alternator lamp can caused by many things, usually it's the brushes worn out, a belts, bad connection- that causes the alternator to intermittently cutout. Check the wiring - including the battery terminals. Very important.

Well as I have written, I have been monitoring it for a while now, both with the vehicle running and when off and the alternator seems to be working fine from the readings I get from when I look manually with a voltmeter. So I think the light is a false positive, at least for alternator charging. In my other threads I detail how the general electrics of the whole van acts in weird ways and thinking this might just be part of it. Still, for peace of mind, I would like an independent voltmeter so I can keep an eye on the voltage without having to go to the trouble of always opening the hood to check myself with the

A modern vehicle has ECU-control and there are many extra reasons for the light to come on. Overheating alternator (plugged vents), voltage too high or low, no output, battery voltage low, overcurrent etc.

You can buy cheap voltmeters for a couple pounds from Aliexpress or eBay etc.

Yea I just saw they have them available from the online electrical shop I use regularly and I have just purchased some other kit so will add one too the cart. Only £3 something. Much better than the overpriced one of almost £20 I linked in the OP!

It is like when I bought usb sockets for my van before I knew you could get them for only a couple of £ from electrical shops. Paid about £50 for a name brand for a 2 port and then months later I see I could have bought bare ones for like £3. 

[electroniclearner820327]

When I tried to get clarity on what was going on, he was defensive, insisting that he was a certified engineer and knew what he was doing, citing service procedures and internal regulations. Eventually, I managed to get enough information from him to understand the root of the problem - and it became clear almost immediately.

This is a problem I have had when trying to get guarantee support for one of my pieces of equipment. The company is famous for its founder being extremely rude to customers. They are very responsive to queries however they have incredible egos about their products such that they ignore data I am trying to give them and just reply with things they think it must be which I already tried multiple times. They told me that 'intermittent problems don't really happen with our products' and so would ignore stuff I was telling them and I knew they were writing it all off as user error.

Looking online it is a love or hate thing with many having similar experiences to me with others never having had issues and singing their praises.

With a lot of fiddling about I managed to figure out the behaviour over the months and make it work despite these issues they tell me cannot exist. It does work well when it works so I am not pushing to get it sent replaced as I know they would also say it works fine. I already sent it back once for testing and they didn't find an issue and so I put it back in and it worked fine for a couple of days and the problems arose again.

The device is very finecky and I have started to find ways to work around its idiosyncrasies.

[SteveThackery]

Sorry but this is a kind of nonsense.
I have been analyzing car electronics and car battery issues for more than 20 years.
You can reliably measure the battery voltage at any point in the car.

Exactly!

@Radiolistener is speaking too theoretically. Yes, you can and will get voltage drops across bits of the wiring loom, but I'm pretty sure @radiolistener has never worked on car electrics because - for the OP's purpose - this is just too trivial to worry about.  Also, someone said that the battery will measure from 13.0V upwards if it is charging. No, it wont. It will measure from 13.8V upwards, but usually significantly over 14V. I've got three cars; one of them reads 14.1V on charge, the other two are 14.4V.

The OP just wants some indication of whether the battery is still being charged when the warning light comes on. A voltmeter plugged into the cigarette lighter socket would be fine for that purpose. We are talking about a minimum of 1V difference between charging and not charging, and most likely 1.5V or more.

The OP can see for himself what the typical readings are between charging and not charging. Switch on the ignition and read the meter. Then start the engine and read the meter. The fault is intermittent, so the OP can see for himself what the typical "charging" voltage is.

Some people in this thread are making a mountain out of a molehill!