Battery Voltage and State of Charge
#1
11-18-2011, 02:42 AM
Battery Voltage and State of Charge
Lots of people think that a reading of 12 volts means a battery is good.
Surprise!
Unlike older vehicles, computer controlled vehicles require the computerised systems to be functional during startup. They are completely intolerant of low voltage.
If you work on your vehicle for a long duration then it won't start ... see above. The drain can come from dome lights, trunk lights, multiple starts, and the system staying awake because the key is always close by. It's a real pain in the you know where if you work where there is no access to plug a charger in.
The problem is exacerbated if your driving pattern consists of short trips and long periods of non-use.
credit: Diagnosing A Car Battery That Runs Down
Surprise!
PHP Code:
12.68v . . . . . . . . . . 100%
12.45v . . . . . . . . . . 75%
12.24v . . . . . . . . . . 50%
12.06v . . . . . . . . . . 25%
11.89v . . . . . . . . . . 0%
If you work on your vehicle for a long duration then it won't start ... see above. The drain can come from dome lights, trunk lights, multiple starts, and the system staying awake because the key is always close by. It's a real pain in the you know where if you work where there is no access to plug a charger in.
The problem is exacerbated if your driving pattern consists of short trips and long periods of non-use.
credit: Diagnosing A Car Battery That Runs Down
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Jumpin' Jag Flash (11-06-2015)
#3
11-18-2011, 08:45 AM
First you need to determine whether your battery is just discharged or if it is dead. If you are driving around, it is probably just discharged.
The chart is a representation of "state of charge".
Charge your battery using a good battery charger at a low rate and see what it looks like. You will probably find that it is just fine. It is just low on charge.
The weakness of computerised high end cars is that they use a lot of electrical power, never fully turn off, and in the case of the Jaguar, may use a less than optimal pulley ratio to keep the alternator revs down. Add daytime running lights and the situation gets even worse.
Combining a battery that is never fully charged with short trips and long period of tinkering eventually leads to a no start because the computer is not getting enough power. The engine cranks just fine. But, no start.
Try charging with a battery charger first before wasting your money.
The chart is a representation of "state of charge".
Charge your battery using a good battery charger at a low rate and see what it looks like. You will probably find that it is just fine. It is just low on charge.
The weakness of computerised high end cars is that they use a lot of electrical power, never fully turn off, and in the case of the Jaguar, may use a less than optimal pulley ratio to keep the alternator revs down. Add daytime running lights and the situation gets even worse.
Combining a battery that is never fully charged with short trips and long period of tinkering eventually leads to a no start because the computer is not getting enough power. The engine cranks just fine. But, no start.
Try charging with a battery charger first before wasting your money.
#4
11-18-2011, 10:10 AM
Veteran Member
I installed this in both my car but I am also installing a regulator to prevent over charging. Solar Battery Charger
#5
11-18-2011, 02:59 PM
Veteran Member
Cold weather kills batteries...
Bingo, I was going to post a thread on this subject...
These car's are super sensitive to voltage. The Jaguar reprogramming software IDS, will not work if the battery is lower than 12.5V steady, meaning most cars wil need a tender/booster/jump for it to perform reprogramming duties, this to me says it all on how important a good battery is.
Now the cold weather is here, an old battery is going to have a hard time booting up the car.
Weird things will happen, out of the ordinary malfunctions will occur, odd messages pop up on the little green screen. Many of these ghosts in the machine will be down to a weak battery.
I learnt this almost as soon as I bought my first 308 - now I have two a Varta and a Bosch, they're exactly the same unit, amp hours, dimensions, and production casting marks. They'll both be Varta - both are used. When I store the car, it's on a tender. The other I make sure is fully charged. Out of bloody mindedness I use the fully charged one to fire the car up, a bit of swapping around every now and again, I don't see odd things any more.
A good point, well raised. Be **** about this very important feature of these cars. A modern battery is now none service sealed for life item. 5 years minimum use, so expect that technology to cost.
UK price for a Varta is £120-£150. Makes a good US battery price of $180-$225
These car's are super sensitive to voltage. The Jaguar reprogramming software IDS, will not work if the battery is lower than 12.5V steady, meaning most cars wil need a tender/booster/jump for it to perform reprogramming duties, this to me says it all on how important a good battery is.
Now the cold weather is here, an old battery is going to have a hard time booting up the car.
Weird things will happen, out of the ordinary malfunctions will occur, odd messages pop up on the little green screen. Many of these ghosts in the machine will be down to a weak battery.
I learnt this almost as soon as I bought my first 308 - now I have two a Varta and a Bosch, they're exactly the same unit, amp hours, dimensions, and production casting marks. They'll both be Varta - both are used. When I store the car, it's on a tender. The other I make sure is fully charged. Out of bloody mindedness I use the fully charged one to fire the car up, a bit of swapping around every now and again, I don't see odd things any more.
A good point, well raised. Be **** about this very important feature of these cars. A modern battery is now none service sealed for life item. 5 years minimum use, so expect that technology to cost.
UK price for a Varta is £120-£150. Makes a good US battery price of $180-$225
#6
11-18-2011, 05:35 PM
It is a very disappointing requirement for owners in cold climates who use their cars in all weather.
In stumbling around the internet, it seems that it is a common fault with other makes. Even downloading tunes to the new Triumph sport bike is fraught with risk if a battery tender is not used.
It's all very puzzling since modern digital circuits run at 3.3VDC with some circuits requiring 5VDC. Surely 10.5 VDC would be enough to supply the power supplies for further regulation.
A 1984 Saab 2 liter will light up in -40C after sitting for months if the battery has enough juice to groan over slowly even just a couple of turns on an old battery. The secret is the mechanical injection. A 1990 Toyota six with EFI will light up in similar conditions with slightly more care.
So, the battery charger bought last year isn't going back then. And the booster cables will have to take up residence in the trunk during high risk months.
The next step is to observe running voltage once the battery is fully charged to see if the alternator is adequate for the task. It is even possible on a XJR that Jaguar opted for a alternator drive ratio that is not so great for around town operation to allow for the possibility that the engine might be operated at high rpm.
Placement in the trunk may also have mandated a lower regulated voltage to alleviate gassing during charge.
Is the original Varta a sealed "maintenance free" battery?
It apparently makes a difference because the optimal charge voltage for a sealed "maintenance free" battery is about 0.45 volts higher than for a regular or "low maintenance" battery. The difference is due to the calcium chemistry. So, matching the original chemistry would be optimal for recovery charging.
Given that the battery can be in a chronicly low state of charge, perhaps the standard advice in the coming months should be to require a known fully charged battery before further exploration. Not take it to a battery dealer and load test, but a full 24 hours on a good charger at a low rate. It could save a lot of time and expense chasing ghosts.
In stumbling around the internet, it seems that it is a common fault with other makes. Even downloading tunes to the new Triumph sport bike is fraught with risk if a battery tender is not used.
It's all very puzzling since modern digital circuits run at 3.3VDC with some circuits requiring 5VDC. Surely 10.5 VDC would be enough to supply the power supplies for further regulation.
A 1984 Saab 2 liter will light up in -40C after sitting for months if the battery has enough juice to groan over slowly even just a couple of turns on an old battery. The secret is the mechanical injection. A 1990 Toyota six with EFI will light up in similar conditions with slightly more care.
So, the battery charger bought last year isn't going back then. And the booster cables will have to take up residence in the trunk during high risk months.
The next step is to observe running voltage once the battery is fully charged to see if the alternator is adequate for the task. It is even possible on a XJR that Jaguar opted for a alternator drive ratio that is not so great for around town operation to allow for the possibility that the engine might be operated at high rpm.
Placement in the trunk may also have mandated a lower regulated voltage to alleviate gassing during charge.
Is the original Varta a sealed "maintenance free" battery?
It apparently makes a difference because the optimal charge voltage for a sealed "maintenance free" battery is about 0.45 volts higher than for a regular or "low maintenance" battery. The difference is due to the calcium chemistry. So, matching the original chemistry would be optimal for recovery charging.
Given that the battery can be in a chronicly low state of charge, perhaps the standard advice in the coming months should be to require a known fully charged battery before further exploration. Not take it to a battery dealer and load test, but a full 24 hours on a good charger at a low rate. It could save a lot of time and expense chasing ghosts.
Last edited by plums; 11-18-2011 at 05:40 PM.
#7
11-18-2011, 06:42 PM
Ahem ...
did a little poking around and came up with this:
https://www.jaguarforums.com/forum/x...83/#post350468
The original Varta is not a sealed "maintenance free" type from all appearances.
So ... if the engineers did it properly, the charging system is regulated for that battery type. The corollary to that is that the charging system is not optimal for a sealed "maintenance free" battery because of the 0.45V difference required by the chemistry.
The charging system designer is also free to optimise terminal voltage for gassing or capacity recovery. Towards 13.5V for lower gassing and towards 14.5 for capacity recovery. A reasonable guess is that the design for a system with a trunk mounted battery would lean towards less gassing for liability reasons.
The implication is that the usual temptation to purchase a sealed "maintenance free" type as a "better" battery is a bad choice because of the difference in charging characteristics leading to chronic under charge. It is almost always a bad choice anyways due to the inability to add water.
The PO purchased a AC DELCO "sealed maintenance free" battery. Nice battery, big battery, wrong type.
That 0.45V is a big deal when skewed in the wrong direction.
There is a way to raise the regulated alternator output by 0.6V, but it requires a couple of big honkin' diodes on heat sinks. Too bad the alternator is mounted down low instead of up top.
did a little poking around and came up with this:
https://www.jaguarforums.com/forum/x...83/#post350468
The original Varta is not a sealed "maintenance free" type from all appearances.
So ... if the engineers did it properly, the charging system is regulated for that battery type. The corollary to that is that the charging system is not optimal for a sealed "maintenance free" battery because of the 0.45V difference required by the chemistry.
The charging system designer is also free to optimise terminal voltage for gassing or capacity recovery. Towards 13.5V for lower gassing and towards 14.5 for capacity recovery. A reasonable guess is that the design for a system with a trunk mounted battery would lean towards less gassing for liability reasons.
The implication is that the usual temptation to purchase a sealed "maintenance free" type as a "better" battery is a bad choice because of the difference in charging characteristics leading to chronic under charge. It is almost always a bad choice anyways due to the inability to add water.
The PO purchased a AC DELCO "sealed maintenance free" battery. Nice battery, big battery, wrong type.
That 0.45V is a big deal when skewed in the wrong direction.
There is a way to raise the regulated alternator output by 0.6V, but it requires a couple of big honkin' diodes on heat sinks. Too bad the alternator is mounted down low instead of up top.
Last edited by plums; 11-18-2011 at 06:48 PM.
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#8
11-18-2011, 07:09 PM
#9
11-18-2011, 07:22 PM
Veteran Member
#10
11-18-2011, 07:27 PM
Veteran Member
My research for an Explorer V8 swap into an '82 Volvo produced a lot of discussion on the battery voltage issue. Apparently, one of the early, mid-80's issues was that the Ford Electronic Engine Control (EEC) issues was that the systems could not tolerate voltage below 10v. That meant even while the battery was dragged down by the starter.
Bottom line is that the Jaguar is sensitive to a poor battery condition.
Bottom line is that the Jaguar is sensitive to a poor battery condition.
#11
11-18-2011, 10:27 PM
#12
11-19-2011, 06:22 AM
the smoking gun ... at least for "maintenance free"
General Motors studied the charging characteristics of lead/calcium batteries and set the voltage regulators of cars equipped with the "Delco Freedom II battery" (ed. one of the earliest maintenance free batteries) at 14.8 volts. Lower settings prevented charging to full capacity.
Older vehicles with voltage regulators set at about 14.0 volts simply will not fully charge lead/calcium or hybrid batteries. Stories abound of cars with older regulators leaving their owners stranded on cold mornings shortly after a "new, improved, maintenance-free" battery was installed. Even two weeks of sitting in the garage, with no load other than the electric clock and burglar alarm, can discharge a battery if the voltage regulator prevented it from being properly charged. (ed. sound familiar?)
The challenge is particularly severe in the case of foreign manufacturers. Many firms are so certain, and so proud, of their engineering expertise that they have declined to modernize their specifications to meet present battery specifications. Bosch, for example, still teaches its "factory-trained" service technicians that 13.8 volts is enough.
Older vehicles with voltage regulators set at about 14.0 volts simply will not fully charge lead/calcium or hybrid batteries. Stories abound of cars with older regulators leaving their owners stranded on cold mornings shortly after a "new, improved, maintenance-free" battery was installed. Even two weeks of sitting in the garage, with no load other than the electric clock and burglar alarm, can discharge a battery if the voltage regulator prevented it from being properly charged. (ed. sound familiar?)
The challenge is particularly severe in the case of foreign manufacturers. Many firms are so certain, and so proud, of their engineering expertise that they have declined to modernize their specifications to meet present battery specifications. Bosch, for example, still teaches its "factory-trained" service technicians that 13.8 volts is enough.
Last edited by plums; 11-19-2011 at 06:24 AM.
#13
11-19-2011, 07:35 AM
Update.
Took my car to the zone where the nice (pretty young lady) did the load test.
1st test was OK but 2nd and 3rd showed a lot lower % charge.
My car did have the factory bat from 2002.
I just noticed a slight hesitation starting when the temp dipped to 35.
When winter kicks in here, 35 is also known as a heat wave!
I live in the frozen tundra AKA Chicago, and replacing the 9 yr old bat seemed the better option.
Got a 750 CCA for 124.
Note- DO NOT LET THE TRUNK CLOSE AFTER REMOVING THE BATTERY!!
Took my car to the zone where the nice (pretty young lady) did the load test.
1st test was OK but 2nd and 3rd showed a lot lower % charge.
My car did have the factory bat from 2002.
I just noticed a slight hesitation starting when the temp dipped to 35.
When winter kicks in here, 35 is also known as a heat wave!
I live in the frozen tundra AKA Chicago, and replacing the 9 yr old bat seemed the better option.
Got a 750 CCA for 124.
Note- DO NOT LET THE TRUNK CLOSE AFTER REMOVING THE BATTERY!!
#14
11-19-2011, 08:09 AM
Senior Member
A Suggestion.
After a few battary/charging issues of my own, I decided to hard wire a battery tender cable to the battery in the trunk of my XK. that way, I don't have to crawl under the rear of the car to clip onto the positive (+) post behind the quarter panel each time I wanted to leave the car on a tender.
Now, the important part. One of the techs on this site told me (and I am now telling you all) DO NOT install the ground side of the tender cable directly onto the negative (-) post of the battery. Instead, wire it to the spare tire hold down post. At first I went right to the ground side of the battery and that somehow "confused" the ECM into thinking the battery was low when it was indeed fully charged. As a result, the car started shutting down secondary systems in an effort to "save" more critical power requirements.
These days, if I am leaving the XK in the garage for more than even a day or to, I simply open the trunk, connect my tender directly to the cable I pre-installed, close the trunk, turn on the juice, and as they say in my home town of New York City..."FORGET ABOUT IT"..
Now, the important part. One of the techs on this site told me (and I am now telling you all) DO NOT install the ground side of the tender cable directly onto the negative (-) post of the battery. Instead, wire it to the spare tire hold down post. At first I went right to the ground side of the battery and that somehow "confused" the ECM into thinking the battery was low when it was indeed fully charged. As a result, the car started shutting down secondary systems in an effort to "save" more critical power requirements.
These days, if I am leaving the XK in the garage for more than even a day or to, I simply open the trunk, connect my tender directly to the cable I pre-installed, close the trunk, turn on the juice, and as they say in my home town of New York City..."FORGET ABOUT IT"..
#15
11-19-2011, 08:37 AM
Veteran Member
#16
11-19-2011, 10:43 AM
Senior Member
There is a conundrum in all this. I take my car off the road over the winter, to avoid road salt damage. So the battery slowly runs down. I start the engine every few days to try to keep the voltage up. This was not entirely successful last winter, and a couple of times I had to hook up a charger.
But in the wintertime, my Jag has to stay outside, and keeping the trunk open to vent the battery during charging, while snow comes down, is not a realistic solution. Besides, leaving the trunk open increases the current draw.
So I'm not sure what the best thing to do is. Maybe disconnect the battery for three months, and recharge it and reconnect it when the weather turns warmer?
But in the wintertime, my Jag has to stay outside, and keeping the trunk open to vent the battery during charging, while snow comes down, is not a realistic solution. Besides, leaving the trunk open increases the current draw.
So I'm not sure what the best thing to do is. Maybe disconnect the battery for three months, and recharge it and reconnect it when the weather turns warmer?
#17
11-19-2011, 10:54 AM
Veteran Member
#18
11-19-2011, 03:30 PM
Senior Member
There is definately a vent tube coming off one side of the battery in the trunk of my 2008 XK Surely, any car designed to hold the battery in the trunk would vent the battery to the outside...
#19
11-19-2011, 03:51 PM
Veteran Member
You are correct but it takes one person that does not know what that tube is for and does not know the importance of connecting it
#20
01-28-2012, 08:54 AM
I bought a cheap solar panel car charger and placed it on rear shelf. Wire can be hidden down edge of rear seat and to right hand kick panel. Then add an aftermarket fused cigarette lighter to the main 12 v terminals there and plug in the solar charger. Less than 5 minutes neat and no permanent modification.
I installed this in 2004 on my xj8 which tends to stay parked up for weeks at a time. Prior to the instalation battery went flat over any 2 week park up period and I ruined a OEM three year old battery. The cheap replacement battery never let me down and lasted 7 years until the day my wife accidentally turned the solar panel upside down. Then two weeks later the battery was deeply discharged and not recoverable.
Hence it seems:
A $20 dollar solar panel charger prevents the discharge on parking and possibly saves more than its cost by lengthening the life of the battery even in winter, even in northern latitudes (daylight 8.30am to 4.30pm).
I installed this in 2004 on my xj8 which tends to stay parked up for weeks at a time. Prior to the instalation battery went flat over any 2 week park up period and I ruined a OEM three year old battery. The cheap replacement battery never let me down and lasted 7 years until the day my wife accidentally turned the solar panel upside down. Then two weeks later the battery was deeply discharged and not recoverable.
Hence it seems:
A $20 dollar solar panel charger prevents the discharge on parking and possibly saves more than its cost by lengthening the life of the battery even in winter, even in northern latitudes (daylight 8.30am to 4.30pm).
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BigMike001 (07-13-2013)
