Modern car intelligent charging systems: Chronically undercharging battery?

[oilboy123]

Get one of the modern barrery testers. You have to measure at the battery with them. On the connectors at the battery is good enough if the connections are clean and tight. Amazon sells them. They are nice to have. I have detected a few batteries of relatives vehicles that neded replaced before they had a no start, by using mine.

The modern battery testers are really nice. They will show the state of charge, actual CCA, internal resistance, voltage, and some also have other features.

It the SOC is > 80 % after sitting unused for about a day, then everything is good.

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Note, my 2016 Honda CR-V will maintain a higher battery voltage if anything electrical ( besides the engine required power ) is turned on such as Headlights, AC, heated seat, sound system. Turn on any one or more and it has a higher idle speed, and maintains a higher battery voltage.

I don't know if other brands do that. But it is something to check.

I was a boat tech for 12 years. I bought one of the "Solar" batt testers. Then I bought another one that shows percentage of charge, and battery health. I used both at work. They work very well.

I took a full river boat battery home from work that I still have about 4 years now. It shows almost perfect health it was a freebie...... I use it as a back up for when the house power goes out on my BPAP machine. I hook up the 12 volt adapter to run my machine. Customer wanted new batteries.

 

[barryh]

I've always made a regular practice of trickle charging a battery when not in use for days or weeks on end and my batteries have lasted anything up to 10 -12 years.

My recently purchased Mk7.5 Golf has a battery condition monitor in the negative battery lead which apparently monitors the charge and discharge current. I'm reading on VW forums that when I connect up a charger or maintainer, a chassis negative should be used rather than battery negative terminal to ensure the charging current passes through the monitor. Anyone care to comment on why the car needs to know I'm charging the battery and would the monitor even work with the ignition off ?

The owners manual is monumentally useless on the topic, simply referring you to the dealer should the battery need charging.

 

[goblin]

Not sure it’s this way with current vehicles but….our 2010 BMW 3 series was supposed to have the “ECM reprogrammed” (?) to allow for charging a new battery...

It does not. It will charge any battery you throw in.
It's just that unless you:

- Register a new battery when replacing with an identical one (Battery registration), or
- Code a new battery when replacing with one with a different capacity (battery coding)

The car's charging system will charge the new battery thinking it's the old one. And it will charge the old one based on how old the car thinks the battery is.

BMWs have an intelligent battery charging system for lower mpg purposes that makes them - in normal conditions - only charge the battery (make the alternator work) on engine overrun or when coasting. The rest of the time the car will power whatever electrical components it powers directly from the battery. UNLESS the battery is low and needs charging, in which case the alternator will charge the battery at all times or almost, till it considers it charged (which is about 80%, it will never charge it to 100%).

So in regular conditions, your alternator basically goes on and off, and it's all electronically controlled.

The topic is an ongoing joke in the bimmerfest forum, as we have a gentleman there who is hell bent on omitting the UNLESS part, and insists that a BMW will never charge a depleted battery even if it's close to dead, unless you're coasting down a mountain or something. And never while idling.

Anyhow, this makes for a quite complex system, which however mostly works, and batteries on BMWs tend to last for a long, long time. I guess most manufacturers nowadays are following suit, as this saves a few drops of fuel.

One way or the other, I wouldn't trust any voltage measurement I take on a modern car unless the battery is disconnected.

 

[barryh]

The topic is an ongoing joke in the bimmerfest forum, as we have a gentleman there who is hell bent on omitting the UNLESS part, and insists that a BMW will never charge a depleted battery even if it's close to dead, unless you're coasting down a mountain or something. And never while idling.

Over a 10 year ownership of my last car I found that when short tripped there was no doubt that the battery always finished a journey at something like 80% charge but over long trips of several hours especially at night it got closer to full charge which is understandable given that under some conditions charging is not shut off at 80% .

Here's one example of an algorithm to convince your "gentleman" I imagine most manufacturers are going to be using something quite similar. It all makes reasonable sense except for what impact supplementary charging will have. One interpretation of the very last section is that any supplementary charging of the battery using a charger or battery maintainer is going to confuse the algorithm into thinking the battery is in a better state than it really is and under charge it even more which makes me wonder if I'm doing the right thing by charging if the car is sat idle for several days or weeks. You have to wonder if all this complexity is worth the very small gains in mpg.



The control module enters Charge Mode whenever one of the following conditions is met:


Under WOT conditions and when the fuel rate (sent by the ECM/PCM) is greater than 21 g/S and the throttle position is greater than 90%.
The headlamps are on, low or high beam.
The wipers are on for more than 8 seconds.
The electric cooling fans are on high speed.
The rear defogger is on.
The battery SOC is less than 80%.
When one of these conditions is met, the control module ramps up the voltage slowly to a level between 13.4 to 15.5V (depending upon the mode of operation the system is presently in) at a rate of 8mV to 50mV per second.

The control module enters Fuel Economy Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 15A and greater than –8A.
The battery SOC is greater than 80%.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 13.0V. The control module will exit this mode once the criteria are met for Charge Mode.

The control module will enter Voltage Reduction Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 2A and greater than –7A.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 12.9V. The control module will exit this mode once the criteria are met for Charge Mode.

After the engine has started, the control module sets a targeted generator output voltage of 14.5V for 30 seconds (Start Up Mode).

The control module enters Battery Sulfation Mode when the battery voltage is less than 13.2V for 45 minutes. Once in this mode, the generator battery control module will set a targeted output voltage between 13.9 and 15.5V for five minutes. The control module will then determine which mode to enter depending on voltage requirements.

In RVC Mode, the control module bases the charging voltage on battery SOC, which is estimated during a key-off event every eight hours, after three voltage measurements every 24 hours thereafter, and then monitored constantly while the ignition is on. These voltage measurements are then compared to estimated battery temperature, as battery temperature vs. battery voltage directly corresponds to battery SOC. While the engine is running, the system uses both the battery voltage and estimated battery temperature to determine the battery current in and out of the battery. The control module then regulates the charging voltage to keep the battery above an 80% SOC.

 

[goblin]

No chance
The gentleman was arguing his point while PROVIDING a document, as proof. Said document was clearly saying:

At sufficient battery charge level, (emphasis mine) the alternator voltage is controlled such that the state of charge remains virtually constant outside the overrun (coasting) phases. The alternator then only supplies the vehicle electrical system.

And also:
The alternator becomes active when the engine switches to overrun or if the battery charge is insufficient.


His position was (quote):

The intelligent generator system with the IBS ONLY charges the battery on overrun, spin down of the alternator on its sprag clutch and / or trailing throttle. ALL other times the alternator ONLY maintains bartery current through the IBS at ZERO, no charging no discharging, carrying the accessory loads.
You can run your BMW 24/7 and it will not replace the current spent starting the motor.

As I mentioned - it's an ongoing joke

 

[D1dad]

All I know is my 09 Altima takes the same alternator as a 2018 that uses the same algorithm as my 21 and 24. All 4 of my batteries are constantly driving around undercharged. Agm of flooded, doesn’t matter. Short tripped is obviously worse but a long drive at 80 isn’t a whole lot better. I never had issue with the cars not starting from sitting any length of time. But, I’ve gotten on board with using a maintainer when not in use. In fact, I’m on the last leg of a 2 week trip for work and both of my cars are setting on chargers as I type this.

 

[nobb]

Doing some more reading, this seems to be a chronic problem with Nissans.

I isolated the battery on it's own to verify that it does test properly and in fact holds a resting charge >12.7V just fine on its own. It's just that when it's hooked up to the car that it seems to stay perpetually undercharged. Strangely though, with the engine on and at idle the voltage is at 14.5V....so I'm not sure how this system is undercharging the battery? Is it limiting the current somehow?

I'm just stumped now as to what's going on. I can't imagine how saving a few amps by not charging the battery could possibly save any noticeable amount of fuel. I wonder if this is the reason they are specifying these EFB batteries, despite the vehicle not having an actual start-stop system. EFB's are supposedly better at lasting longer even under partial charge conditions. Although I can't imagine this to possibly be good for long term longevity.

 

[goblin]

...I'm just stumped now as to what's going on. I can't imagine how saving a few amps by not charging the battery could possibly save any noticeable amount of fuel...

If memory serves - it's disconnecting the alternator via a clutch - that's what saves fuel by getting some friction off. At least - that's how it is on BMWs.

Not sure how Nissan handles it, and how it compares with BMWs system, but my guess would be most are handled in a similar way nowadays.

BMW does flat-out recommends to put the car on a charger if not in use for more than a couple of weeks. And it will only allow charging the battery to 100% in very rare cases, if ever. It will usually keep it at 80%ish.

Also, not sure if Nissans require a registration of the new battery after a swap, but if your original ones were holding fine then the subsequent ones didn't - that could be it. The system benefits from knowing a new battery has been dropped in. If it still thinks it's the old one, it takes its age into account.

Again - that's how BMW does it, but I suspect any intelligent charging system would do that.

 

[nobb]

If memory serves - it's disconnecting the alternator via a clutch - that's what saves fuel by getting some friction off. At least - that's how it is on BMWs.

....

Wow, an entire clutch on the alternator? That just seems like one extra part that will eventually wear out and fail. These silly designs to save fuel are just silly now because you're not really saving money in the long term when you inevitably have to diagnose or replace these parts.

There's definitely no alternator clutch on this vehicle. I may have to log the voltage through OBD and see how it varies throughout a drive. Some people on other forums are saying the voltage varies depending on the driving condition (eg. voltage dips during acceleration to not charge the battery, vice versa during deceleration).

Luckily there does not appear to be any battery registration procedure after a swap.

 

[goblin]

...There's definitely no alternator clutch on this vehicle...

https://www.nissanclub.com/threads/alternator-clutch-fail.330387/

Possibly a sprag clutch. Like the freewheel mechanism on a bicycle. Om a BMW you can definitely not see it and it looks like a normal alternator.

Now, are all alternators like that, and a BMWs alternator has some electronic control on the clutch, or are all clutched alternators electronically controlled - I don't know.

But the mention in the link above about the clutch decoupler tool hits home, as BMWs need such a tool as well.

 

[nobb]

https://www.nissanclub.com/threads/alternator-clutch-fail.330387/

Possibly a sprag clutch. Like the freewheel mechanism on a bicycle. Om a BMW you can definitely not see it and it looks like a normal alternator.
...

Learned something new today. I looked at the pulley and you're right it does look like there is a sprag clutch assembly. Does not appear to be any other electronically controlled clutch. This probably isn't what's causing the issue though.

Starting to feel like there really isn't anything I can do about this except suck it up and drive it as is. The EFB battery is 1 year old and to be fair, doesn't seem to have any abnormal degradation yet. This just seems to be how Nissans designs their electrical systems. Probably just need to do an equalization charge atleast once a month to keep the plates clean.

 

[tcp71]

On the F150 there is an induction sensor for the smart battery system. Unplugging the connector at the ring reverts the system to normal (old timey) operation. There is a code in the OBD system that is set by this, but it doesn't trigger a CEL or cause issues.

 

[nobb]

On the F150 there is an induction sensor for the smart battery system. Unplugging the connector at the ring reverts the system to normal (old timey) operation. There is a code in the OBD system that is set by this, but it doesn't trigger a CEL or cause issues.

Have you measured the voltage before and after? I wonder if disabling this would result in overcharging. Flooded is more tolerant than AGM to this, but I would take having to add water once in a while over undercharging.

 

[tcp71]

On the highway the battery voltage shown on my scangauge varies from 12.1V - 14.3V depending on what the BMS is doing - with the sensor connected. Without it connected, it just runs at 14.2V or so.

 

[nobb]

So I put a plug in voltmeter to monitor things and here's what I noticed:

Cold start, idle, no load: 12.0 - 12.3 V
Cold start, idle, with load (HVAC fan, lights, heated seats on): 12.8 V
Accelerating or normal driving: 13.9 V
Decelerating or braking: 14.9 V
Warm engine, idle or park: 13.9 V

So it's very obvious the variable voltage system is trying to optimize for fuel savings. On first start while idling, it's basically not immediately charging. When driving, it's barely charging...more of a trickle or float charge. Keeping as little load on the alternator as possible to save fuel. Only during braking/deceleration does it attempt a pseudo regen with the battery taking on a charge.

So probably the average battery state of charge may depend mostly on driving habits. It's seemingly kept mostly only 60 - 70% full to allow room for these pseudo regen cycles to recapture energy. IMO this is really stupid...how much fuel is this really saving.

This is probably why they spec an EFB battery. Since they are more tolerant to being partially charged. I have no idea how this behavior will affect longevity but I can't imagine it to be good. If the battery was ever replaced with a flooded unit, I can't see them lasting more than 2-3 years in this application. EFB or AGM batteries are 50% more expensive than flooded.

 

[chexxers]

TOOOO much tech these days, thats why my newest is an 11 pickup, car is 2001 + a garage queen + battery is on a quick disconnect unless driving + both get toped with a C-Tek charger. replaced truck bat at 10 YO just because, car alternator went out + replaced it + the 9 YO battery all is well!!

 

[Wheel366]

Does anyone else notice the ransom note similarities with some recent posts? Not just in this thread. Did the other get blocked?

 

[f355spider]

I've always made a regular practice of trickle charging a battery when not in use for days or weeks on end and my batteries have lasted anything up to 10 -12 years.

My recently purchased Mk7.5 Golf has a battery condition monitor in the negative battery lead which apparently monitors the charge and discharge current. I'm reading on VW forums that when I connect up a charger or maintainer, a chassis negative should be used rather than battery negative terminal to ensure the charging current passes through the monitor. Anyone care to comment on why the car needs to know I'm charging the battery and would the monitor even work with the ignition off ?

The owners manual is monumentally useless on the topic, simply referring you to the dealer should the battery need charging.

BMW marketing literature claims the IBS is working even with key off on the ignition. It monitors voltage every few minutes I believe is what it said.

No one really knows about using a battery maintainer...not even the dealers. On my 2018 BMW (with IBS), it has two batteries. An H9 AGM in the trunk and a H5 in the engine compartment. The IBS is only present on the trunk mounted battery, and BMW recommends to only connect a battery tender to the jump start connections in the engine compartment to maintain the H9 battery. They make no comment about maintaining the H5. I believe on my BMW the H5 powers the car when using the "stop start" function and the car engine is off during a stop. The H9 is then used to restart the car. I have this function disabled using bimmercode app, and the "start stop" function is only active in ECO mode now.

On a bimmerfest thread (6 series) a user said both the dealer and BMWNA told him not to connect a battery tender to the H5 battery in the engine compartment as they believed that could back flow to the IBS and damage it. He tried and said it was not damaging anything. So much for the warning.

I used a battery tender and alternately charged both batteries (seperately), using the jump start terminals for the H9 AGM and connected directly to the H5 AGM battery. I did this for several months without issue. At that point, I didn't want to keep opening the hood each time to connect up battery maintainers, and didn't want to charge them seperately, or have to tie up two battery tenders, so I wired up a Battery Minder Y adapter to the H5 and jump start terminals and ran the cord out the back of the hood by the passenger wiper blades. My Battery Minders are rated to maintain up to 8 batteries at a time as long as they are reasonably fully charged. Been working for close to three years without issue. My Granite Digital "Battery Saver" battery tenders are also rated to maintain multiple batteries.

https://www.batteryminders.com/multiple-battery-connector-210-AY

The batteries are original in my BMW and now 7+ years old. The car only has 17k miles so spends most times on a battery tender.

 

[hardheaded]

My 11 Tahoe has that system. I quit looking at the voltage gauge in the truck because it looks as if it is under charging the battery. Drove me crazy at first. I carry a jump pack with me. i hate all this new electronic crap.

 

[f355spider]

My 11 Tahoe has that system. I quit looking at the voltage gauge in the truck because it looks as if it is under charging the battery. Drove me crazy at first. I carry a jump pack with me. i hate all this new electronic crap.

The technology seems to work just fine for the majority of car owners. The issue is with the outliers. People that constantly short trip, or folks like me that simply don't daily drive their car (I have one primary daily, and two other "fun" cars that sit a bunch).

If the car is driven at least a few times a week at some reasonable distance its totally fine and seems to offer some benefits in marginally better gas mileage and longer battery life. My solution is to simply connect up a battery tender whenever I pull my cars into the garage. I have installed ring mounts on my batteries and conveniently located the plug to make it an easy process. No opening hoods or attaching clamps to the batteries.