Battery State of Charge data poll.

drivesafe

Active Member
Hi folks, if any of you have the time, and have access to a digital multi meter, would you kindly take part in a simple battery voltage test.

The idea of the poll is to see whether cranking batteries are not being charged above the 70% level that is proposed in quite a few articles or is it more like 90+% as I have posted about.

There are 10 basic questions and just answering the first will do, but if you have the time and info available, answers to any or all of the other nine would be very helpful in see just how alternator battery charging works in different vehicles.

The first question will be more accurate the longer the vehicle's motor has been off, preferably 12 or more hours after the motor was last on.

1 ) Once the motor has been off for a few hours, preferably 12 or more, what is the voltage at the cranking battery’s terminals.

2 ) Type of vehicle.

3 ) What make and type of battery ( a model number will do )

4 ) When was the last time the vehicle was driven.

5 ) How long was the last drive

6 ) Is this your day to day drive or a once a week vehicle

7 ) Alternator size

8 ) Is this your tow vehicle or other.


If you can, the following info would also be of interest.

9 ) What is the voltage at the cranking battery about 1 minute after you first start your vehicle ( cold start )

10 ) With the motor still running, what is the voltage at your cranking battery after a 30 minute drive.


The last two questions are for gaining a better idea of how different alternator operations. Alternator operation in most vehicles is now controlled by the vehicle’s Engine Management Computer. This independent control not only means that there will be differences in alternator operations between vehicle makes but even between same make and models.

I Had an 03, Mark III Range Rover, first version of the current model. It’s alternator went to 14.3v soon after the motor started and stayed there for as long as the motor was running.

I now have an 08 Mark III Range Rover, the latest version of the current model. The alternator in the 08 RR does not start generating power for about 30 to 50 seconds after the motor is first started and the initial voltage can then be anything from 14.2 to 14.9 volts and does not seem to be influenced by ambient temperatures.

Exactly 30 minutes after the first start, the voltage lowers and can be as low as 13.2v.

So info on how the different alternator operations would be interesting to see.

For anyone trying to get any form of alternator operations info, it is almost impossible to get any data form any of the manufacturers, so your input can be very helpful.
 

drivesafe

Active Member
An example of info entry

This is an example of the type of data collected, this is the info from testing Subaru Forester

1 ) Once the motor has been off for a few hours, preferably 12 or more, what is the voltage at the cranking battery’s terminals.
1 ) 12.62v

2 ) Type of vehicle.
2 ) Subaru Forester Sports

3 ) What make and type of battery ( a model number will do )
3 ) Make? Type = 55D32L = 48 A/H Flooded Wet Cell

4 ) When was the last time the vehicle was driven.
4 ) 16 hours

5 ) How long was the last drive
5 ) 25 minutes

6 ) Is this your day to day drive or a once a week vehicle
6 ) Daily drive, average drive time is 45 minutes

7 ) Alternator size
7 ) 110A

8 ) Is this your tow vehicle or other.
8 ) Shopping trolley and to and from work transport

9 ) What is the voltage at the cranking battery about 1 minute after you first start your vehicle ( cold start )
9 ) 14.55v 1 minute after a cold start

10 ) With the motor still running, what is the voltage at your cranking battery after a 30 minute drive.
10 ) 14.32v after a 25 minute drive
 

bmurray2250

4x4 Earth Contributer
1 ) Once the motor has been off for a few hours, preferably 12 or more, what is the voltage at the cranking battery’s terminals.

11.83V

2 ) Type of vehicle.

Toyota Prado VX 3.4L Petrol 1998

3 ) What make and type of battery ( a model number will do )

Supercharge Allrounder MRV48 (same as the Aux)

4 ) When was the last time the vehicle was driven.

Sunday 20/9/2009

5 ) How long was the last drive

25 minutes

6 ) Is this your day to day drive or a once a week vehicle

Day to day but I work from home so it can sit for a few days without being driven

7 ) Alternator size

80A

8 ) Is this your tow vehicle or other.

Yes but I rarely tow

9 ) What is the voltage at the cranking battery about 1 minute after you first start your vehicle ( cold start )

13.8V

10 ) With the motor still running, what is the voltage at your cranking battery after a 30 minute drive.

12.8-13.4V depends it in a charge cycle. Rotronics LED comes on
 

drivesafe

Active Member
how many forums are you putting this on drivesafe

Hi newhue, about 15 to 20, I’m not sure and I will have to take count of them so I don’t forget to check them all.

I have about fifty replies so far, with some sites not replying, others like here are just starting to and others have up to 14 replies so far.


Hi and thanks for the info bmurry2250.
 

drivesafe

Active Member
Every time i put a multi meter near 12v DC it blows the sh#t out of it.
Hi teza, do you by any chance have your meter set up to test amps.

Because if you do, when you check volts, you create a dead short.

Just make sure your test leads are plugged into the correct input.

Cheers and best of luck.
 

drivesafe

Active Member
Thanks to those who took part in the poll and I am not going to post up any opinions on the results, people can come to their own conclusions.

Anyway here is the initial results from 52 replies of the Cranking Battery Voltage reading are as follows :-

95% ( 12.6 ) or higher = 25

90% ( 12.5 ) or higher = 13

80% ( 12.42 ) or higher = 4

70% ( 12.32 ) or higher = 2

Lower than 70% ( 12.32 ) = 8

There is a lot more data to be sorted yet but this was the main aim of the poll.

The Highest reading was 12.95v and the lowest was 11.83v

A small number of the reading were taken less than 12 hours from the last time the motor was run so I will have to do some calibrating.

Again Thank you to all those who contributed.
 

drivesafe

Active Member
Myth Busted

Some more info from the poll, and there are still replies coming in.

Most but not all replies included the operating voltage, of the info supplied, only 6 had 14.5v or higher, nearly half the vehicles ( 23 ) were between 14 and 14.4v but more interestingly though, 21 were under 14v but most had a cranking battery SoC of higher than 90%.

Some additional info, and this was to be expected, 6 of the vehicles with cranking battery SoC of less than 80% were pre 2001, 2 were 2001 Jeeps and these also had operating voltages of just 13.9 Max, 1 vehicle was 2003 and the last was 2006.

Of the vehicle with 90% or better cranking battery SoC, 14 were 2002 or later, but 13 were pre 1999 and of these 4 were pre 1990.

This well and truly makes a mockery of the myth that you can’t charge a cranking battery over 70-75% SoC and it shows that the alleged problem probably never existed.

BTW, could everybody add the make year of your vehicles when replying.

It’s been interesting to see how any older vehicles had good battery stats

Cheers.
 
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rodw

New Member
Sorry, I missed this post. I had a look at mine this morning which was only driven for 5 minutes over the weekend.

Cranking Battery 12.46 volts (> 90%)
Auxillary Battery 11.61 volts (< 10% - According to this link Battery Metering which also says voltage is the least accurate method to measure SOC)

These batteries are the same age as the dual battery went in straight after I bought the car new.

While the results of the poll is interesting, it is not much use for those of us interested in maintaining an AUX battery in top condition to keep the beer cold for extended periods. The cranking battery hardly ever gets discharged and is usually close to fully charged in a few minutes. The environment of the two types of batteries is totally different.

My AUX battery was fully charged last Friday week and then had three days use camping not driving and last Friday, I left it run for a couple of hours so I could defrag the HDD of my Car PC. This meant my amp and Car PC Power supply were on and both have 20 amp fuses, so they draw a bit of power. My drive to work 35-40 minutes each way and the ECU reports a voltage of around 13.3 volts after 30 minutes (as reported by the ECU via OBDII software). I can also monitor the voltage of the system while driving by the volt meter in my GME UHF. It seems to be out a bit as it is always 0.2 volts lower than the battery terminals or the ECU reading. From this, I conclude that the ECU reading is an accurate measure.

In a week after a deep discharge and one hit for a few hours 3 days ago, my AUX battery has not really improved yet I know it can get to 95% SOC with an external charger. The vehicle charging system is fine given the SOC of the cranking battery.. From my recent experience, I think the charging system is capable of maintaining the AUX battery at 90-95% SOC, but can't get it back up there after a deep discharge.

I'll try and remember to look at the voltage of the AUX in the morning to see if a days driving has had an impact.

I think it would be really interesting to compare the voltage of my AUX battery voltage after 12 hours standing still with BMMurray's as I have an ARB smart Isolator and he has the Rotronics DC-DC charger. So mine is charged by the standard vehicle charging system, his by a smarter DC-DC charger.

So come on BMMurray, post up the voltage of your AUX battery.
 
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drivesafe

Active Member
Hi rodw, The chart you posted the link to is for measuring the voltage on an open circuit battery, batteries in vehicles, even with everything turned off still have a load connected to them so you need a load SoC voltage chart like that below.

600573_SoC_Table.jpg


Testing of the auxiliary battery is probably going to be another test.

Cheers.
 

rodw

New Member
Thanks mate, You'll need to be careful with AUX batteries then because in many instances the AUX will be able to be measured with no load but in my instance there is a small parasitic load on the AUX battery for the regulated smart power supply for my Car PC. Your tbale certainly looks better.

I am not so sure the myth is busted yet, talking to BMurray today and his AUX battery has a higher voltage than his cranking battery! That has never been possible with my car even when it was new! The Hilux and Prado have essentially the same engine etc, but the Hilux gets a 100 amp alternator (25% larger than his). The difference must be attributable to the different AUX charging systems (Rotronics v's ARB) as my AUX battery is capable of holding 100% SOC with a mains powered charger.
 

drivesafe

Active Member
Hi again Rodw, yep a bit more involved when testing auxiliary batteries and in your case with your set up, if your not going to be using the auxiliary battery for a few days, try disconnecting the negative terminal off the auxiliary battery and just use your 4x4 as usual.

BTW, leave your positive lead connected to the auxiliary battery for safety reasons.

In two days time, use the chart that you posted the link to to measure the SoC voltage of your auxiliary battery.

Hope this helps you, cheers.
 

rodw

New Member
Not really feasible to disconnect the AUX. it does a lot more than just run a fridge. Anyway, I'll monitor it during the week if I remember. This morning I measured:
Cranking Batery 12.53 Volts
AUX Battery 12.23 volts

It will be interesting to see where the AUX voltage plateaus out. Then I will try and charge both batteries from the mains and see if it will improve on the car charging circuit.
 

rodw

New Member
Well, it's Friday and my aux has finally caught up with the cranking battery in the voltage stakes;
Results for the last three days:
Wed - Cranking 12.49 Volts, Aux 12.35 Volts
Thur - Cranking 12.53 Volts, Aux 12.51 Volts
Fri- Cranking 12.53 Volts, Aux 12.53 Volts

It looks like the cranking battery has stabilised and the Aux battery has caught up with it. So according to your table, both batteries have got to 90% State of Charge.

I decided to test the batteries with a Hygrometer, you know, one of these:
986658_hygrometer.JPG


Hygrometers measure specific gravity which is the traditional way of measuring battery state of charge of wet cell batteries, much more accurate than voltage without a load. This tells a very interesting and different story:

Cranking battery - 1305 - almost off the green (fully charged) scale, 100% State of Charge
AUX battery - 1190 - still in the red (discharged) scale, about 35% State of Charge

Somehow, I don't think the myth has been busted yet.:( Measuring the voltage to determine battery state of charge is very simplistic and clearly inaccurate. So tonight, I will stick the smart charger on and see what specific gravity the AUX battery is capable of holding and report back.
 
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drivesafe

Active Member
Somehow, I don't think the myth has been busted yet.:( Measuring the voltage to determine battery state of charge is very simplistic and clearly inaccurate. So tonight, I will stick the smart charger on and see what specific gravity the AUX battery is capable of holding and report back.

Hi Rodw, how did you go with the SG test after you charged the battery?
 

drivesafe

Active Member
Hi folks and the poll is now closed.

Thanks for all the replies, and while I had hoped to get 20 to 25 replies but there are some 61 replies and thats excellent.

Owing to some dubious one eyed comments made on a number of sites, the poll results are being compiled by someone else and once the results are available I’ll post them up.

The poll has been a very good chance to show many people just how bogus this 70% myth is and the fraudulent lengths some are prepared to go to to protect this myth.

Thanks again.
 

oldrtack123

New Member
his tells a very interesting and different story:

Cranking battery - 1305 - almost off the green (fully charged) scale, 100% State of Charge
AUX battery - 1190 - still in the red (discharged) scale, about 35% State of Charge determine battery state of charge is very simplistic and clearly inaccurate. So tonight, I will stick the smart charger on and see what specific gravity the AUX battery is capable of holding and report back.
Hi Rod
I may be jumping the gun ,BUT I think you will find that the aux is on the way out.!!!
The readings you got are quite likely with a battery with reduced capacity due to age etc
At rest volts is the industry way of readily determining battery S O charge[ not % of marked capacity ]
For wet cells the SG test is an additional test & may reveal a battery with lost capacity & shorted cells
.However not practical with sealed batts where @ rest volts is the ONLY readily available guide
 

omvanders

New Member
What about the difference between the Calcium batteries and the usual 'old' wet cells?

Aren't the Calcium units much fussier with how they are charged [hence the need for me to buy one of those new (& expensive !!) fandangled chargers]?
 
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