What's a normal rest voltage for a US car battery in a car?

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50ma? - sigh.

The Victron is already 'out for delivery' today and putting a meter inline - the amps jump >10a when the console is powered.

Part of this is to monitor the draw but also monitor WiFi+OnStar while camping with bad cell reception (many hours hopefully) and how it affects the battery. I like the idea of monitoring the battery as the vehicle sits in the garage. I can also re-purpose it for the trailer if it's useless for the rig.

Fuses - I read about this and someone even mentioned a diode shorting in the alternator causing a draw and unplugging the alternator to check this - but I'm reluctant to go this far personally vs taking it to a shop.

At this point, I mainly want to understand *exactly* what's happing but for ongoing use I need to find a permanent / industrial strength mount point.
 
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OffGridInTheCity said:
Part of this is to monitor the draw but also monitor WiFi+OnStar while camping with bad cell reception (many hours hopefully) and how it affects the battery. I like the idea of monitoring the battery as the vehicle sits in the garage.
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Got it. I do believe that this production version has a place for a 2nd battery. There should be an open place drivers side front by the Washer fluid fill. There may also be an "OEM" kit that can be purchased. Most of the time it is fitted with a deep cycle battery to power the accessories when not running. Just a thought if you are camping.

Wolf
 
I have no clue what you are all talking about.
But back in the day when we (with my ex) had a camper(vw type 2 and a Chevie nomad 20 extended after.) i had 2 separate batteries.
One for the engine and one for light, fans, cooler, shower, water pump, coffee maker, hairdryer ect.
Oke 40 years ago...how tech changed.
Must be honest: with one large water tank and a large extra gas tank (second one) for heating water and gas.....

You have a lot of 18650 and a lot of knowledge...use it, i did not have back then 18650 or lto cells, just deep cycle lead acid.
Do i miss something?
one start batt and one for the go to camping batt.
 
TOTAL RESET in my thinking. We are retired and we go long periods where we driver our cars once-a-week to grocery store kind of thing. Prior to getting the Yukon, we didn't worry about this - they maintained enough charge / cars start every time sitting a week.

It was my focus on this 'new' (used Yukon) that made me assume that 12.1v was somehow a serious issue. Then I completely misread the rest draw amps on my 20yr old meter and then went off on a tangent - e.g. this thread to a large degree.

Some Facts:
- I've been measuring my old 2004 Cadillac SRX battery voltage. This vehicle has done several years driving once-a-week. Guess what? after a week the voltage is ~11.9v. After the trip to the store, the next day it's 12.3v. And then it pull down to 11.9v after a week.

- Yukon is actually pulling 2-3w (not 40w). 2.5w/12.2v = ~200ma or 0.2a. This is consistent with the Cadillac SRX above.

Conclusions:
- While my car batteries do go low (11.9v) after sitting a week, this seems to work multi-year and once-a-week driving and the Yukon is simply following a similar pattern.

- I'm surprised to learn that 1) I'm abusing the batteries by starting the cars at 11.9v and 2) BUT the batteries don't seem to care that much as they last ~5yrs.

TMI: I did get the Victron shunt but it's pretty darn large/difficult to easily mount for industrial strength. Besides, the voltage readings and discharge curve are good enough to estimate battery draw for my purposes. So I've ordered a bluetooth voltage monitor - https://www.amazon.com/dp/B07WCW49YM - which should easily mount under the batter cover. Once I get data I'll post some graphs.
 
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Installed the bluetooth voltage monitor....
Here you can see the Victron 1000a shunt sticks up and after looking around, didn't see a nifty easy mount.
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whereas the ANCEL battery monitor is small enough to fit right under the battery cover and I feel like it can ride safely within the plastic cover.
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The app auto-detects the monitor showing battery voltage... I don't have to open the hood or even go into the garage
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The app stores 31days of data but it thinks that 12.23v = 37% DOD which seems off to me based on voltage discharge charts I've seen.


@Wolf as a side issue, you mentioned the possibility of a 2nd battery but the the 2021 6.2L Yukon Denali doesn't have the holder.... too bad for me as I had my hopes up for just a moment.
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Ahhhh, so it looks like it might have to go through a few cycles to *learn* what the battery chemistry is. That stinks

Checking link....

6 - 20V !?!? No wonder it's confused if it thinking 20V is full charged. So yeah, looks like it needs to run for a bit to understand what the real voltage range is of that particular battery.

OffGridInTheCity said:
The Victron is already 'out for delivery' today
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I thought you were getting a Victron battery monitor. Maybe I misunderstood your comment earlier.
 
Korishan said:
I thought you were getting a Victron battery monitor. Maybe I misunderstood your comment earlier.
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Yes I got one. The 1000a is large and heavy and I'm not seeing a good way to mount it / run custom cabling in the engine bay in a simple + industrial strength way.

This cheaper voltage-only will serve my purposes.
 
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My 23 years old Scoda Octavia 1.9l Diesel draws around 20...30 mA just standing. After freshly charging the battery its about 12.8V up to 24h later. It slowly drops to 12.65 ... 12.7 the next 7 days. Lower than 12.5 V is already bad as lead sulphate builds up and crystalizes in bigger junks.
When the car draws 500 mA thats way too much - there must be something wrong. But you have to measure 10 min. after last using the car or closing all doors etc.
 
The bluetooth, battery voltage monitor over 48hrs of the rig sitting in the garage is showing this....
12.15v down to 12.09v after 48hrs = 0.6v drop.
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Using a car battery discharge charge like this we get 10% SOC drop over ~1.1v.
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0.3v is 27% of 1.1 - so let's say I have a 2.7% SOC drop over 24hrs.
2.7% of 80ah = 2.16ah * 12.15v = 26.2w / 24hrs = 1.09w/hr / 12.15v = ~89ma battery draw.

So I don't have a (major) problem! and I'm going to put this to bed :)

TMI: I like this app - and to be able to approach the car from inside the house and see the battery voltage.
 
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Imho 12.5 V for a 12V lead acid battery with no load is not 90% SoC, its more around 50%. 90% might be correct under a load of 5...10 Amps.
Below 12.6...12.5 V lead sulphate builds up - this is bad for your battery. When standing for a longer time it should be above 12.6V. The battery may be worn off or something else is wrong here! I use a little laptop charger that delivers 20V and a DC buckconverter in my garage to contantly charge (trickle charge) the battery around 13.8V. If i disconnect the charger the battery voltage stays above 12.7 V for the next 7 days. When it drops below, i reconnect the charger.
 
batteryuniversity.com

BU-804b: Sulfation and How to Prevent it

BU meta description needed...
batteryuniversity.com batteryuniversity.com

Sulfation occurs when a lead acid battery is deprived of a full charge. This is common with starter batteries in cars driven in the city with load-hungry accessories. A motor in idle or at low speed cannot charge the battery sufficiently.
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What is sulfation? During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline and deposits on the negative plates. This leads to the development of large crystals that reduce the battery’s active material, which is responsible for the performance.
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reversible sulfation can often be corrected by applying an overcharge to an already fully charged battery in the form of a regulated current of about 200mA. The battery terminal voltage is allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on a 12V mono block) for about 24 hours. Increasing the battery temperature to 50–60°C (122–140°F) during the corrective service further helps in dissolving the crystals.
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BU doesn't mention what voltage directly, but mentions "deprived of a full charge". So I would take that as anything <90% SoC at least.
I was thinking of an easy way to do what paddy72 was saying, plugging in a battery maintainer.
If you take a connector and use 4 neodymium magnets and put them into a form in pairs with reverse polarity, you could make a connector that is safe to drive away with while still connected and not do any damage to the vehicle. Basically a vehicle sized MagSafe connector.
Charging at about 200mA would be far low enough for the magnets to transfer the energy w/o overheating or causing too much resistance/drop in the transmission lines.
 
Korishan said:
If you take a connector and use 4 neodymium magnets and put them into a form in pairs with reverse polarity, you could make a connector that is safe to drive away with while still connected and not do any damage to the vehicle. Basically a vehicle sized MagSafe connector.
Charging at about 200mA would be far low enough for the magnets to transfer the energy w/o overheating or causing too much resistance/drop in the transmission lines.
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Interesting. I like the break-away aspect!

You say to yourself it's OK for a one-off (like leaving a charger connected to a car) but one forgets. I've had a couple of recent bad occurrences while moving my vehicle and trailer improperly. In one case I planned to move the car only 2" so I left the 7-way connected and wound up ripping it out of the socket as I moved 7". And I recently left the step stool along side the trailer door and somehow ran over it with tires only moving 4 feet - Yikes. It's not good practice to leave things improperly connected :)

I did a search for wireless car battery (maintainer level, even 100ma would be useful) charging - but of course nothing comes up. Seems like a Shark Tank opportunity for someone to develop something. I read about floor mats you can drive over for EV charging or maybe something you could hang from ceiling like a tennis ball that is hovering over the battery when parked but safe to pull the rig in/out that could bridge the power transfer gap.
 
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Folks - I wound up buying a battery tender for my Yukon - https://www.amazon.com/dp/B01L0HTX72 - because it drops to 12.0v after a 5 days and it can be 14 - 21 days between driving it right now.
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It gradually went up to 14.5v thru yesterday/tonight but then after full-charge appears to have stabilized at 13.0v this morning - e.g. does this sound right for long term float?

Just trying to understand better - quite different than 18650 NMC. After driving the rig hundreds of miles, the battery settles right back to 12.5v within an hour and then drains from there. 12.7v is full charge per google charts so is 13.0v a normal float voltage? I would never do >4.2v for float for 18650 and it just bothers me :)
 
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OffGridInTheCity said:
It gradually went up to 14.5v thru yesterday/tonight but then after full-charge appears to have stabilized at 13.0v this morning - e.g. does this sound right for long term float?
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Yeah, that's fine. It's possible the battery tender only comes on once the voltage drops below a set point. This would possibly be why it stabilized at 13V.
Lead acid is a whole different animal from Lithium based batteries. It handles the high float just fine w/o issues. This is for several reasons. Lead Acid has a self discharge higher than lithium for instance. Also this higher SoC also helps to keep Sulfates from building up on the plates.

If you monitor the input voltage from the charger, and the battery voltage, you'll notice that the charger is continually dumping amps into the battery, even if the battery isn't connected to anything at all. And this is because the lead self discharges
 
I have one of the victron 12v/10 amp ip65 smart chargers that will eventually get mounted in my pickup to run when the block heater turns on at night. I have it keeping one of my vehicle batteries in long term storage mode. It keeps it at ~13.5v and then wakes it up once a week with a higher voltage push to keep the battery happy.
 
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