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Here’s a screen shot of my XC90 battery charge state over a few weeks in Summer this year. You can see when the car was driven more, and when it was driven less.



Every time the graph shows the charge increasing at a positive rate, the battery is charging. Negative means discharging. You can clearly see that some drives charge the battery somewhat, but not back to 100%
You can also see when I charged the battery on the 30th July, when it moved quickly up to 100%. You can see that after that charge, the average charge state stayed well above 80% for a week or so, then dropped, and slowly started coming back up.
You can also see on the 18th June that a negative dip occurred, and then the battery recovered/was charged, but only back to where it was, just under 80%.

Such data is invaluable when wanting to understand your battery charge state and when diagnosing a problem with charging systems and then battery.


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Here’s a zoomed in view of August where I was on holiday and we drove 3hrs to our destination, and then used the car nearly every day. Before we left on holiday I had charged the battery to 100% using an overnight charge. The charge state varies, but stayed high You can see that with daily use the charge state is never constant and does vary a lot, but as long as your battery stays above 60%, it is considered good. Such variation is typical for a lead acid battery in normal use.




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And one further note: nothing is perfect in this world. The CTEK Battery Sense cannot measure the specific gravity of the acid in the battery. Instead it performs estimations because it knows the following:
1. When the battery is being charged (voltage goes to 14V or so)
2. The battery temperature (the battery sense is mounted next to the battery, and charge rate is temperature dependent)
3. The size of the battery, in AH (entered by you in battery sense)
4. The voltage drop curve of the battery (monitored when the battery is not charging)
Based on all the above, it performs a battery charge state calculation which gets better over time as it gathers more data.


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Discussion Starter #44
And one further note: nothing is perfect in this world. The CTEK Battery Sense cannot measure the specific gravity of the acid in the battery. Instead it performs estimations because it knows the following:
1. When the battery is being charged (voltage goes to 14V or so)
2. The battery temperature (the battery sense is mounted next to the battery, and charge rate is temperature dependent)
3. The size of the battery, in AH (entered by you in battery sense)
4. The voltage drop curve of the battery (monitored when the battery is not charging)
Based on all the above, it performs a battery charge state calculation which gets better over time as it gathers more data.


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Thank you so much for the really informative and helpful advice! I really, really appreciate it!

My car's battery is in the back so won't be able to test load without unlocking the car - unless I disconnect the negative after fully charged with a charger and see what readings I get after a day or two.

Earlier today I drove it to do grocery shopping - for the first time after the problem earlier this week (and after I cleared codes with VIDA) - battery was fully charged about 36hrs ago and the car started / drove with no issues - in heavy rain so headlights and all gadgets were on - it was a short trip to the supermarket after after reaching home I did a bunch of things with doors open and shifted seat positions for a good 20mins. At this point the cigarette lighter battery device arrived, so I plugged it in - read 12.1v. When I shifted seat position again it went down to 11.8 before reaching back to 12.1 again when I finished.

I'm going to buy a CTEK battery sense as recommended. My charger is CTEK 7000 (it's an old one made in Sweden and functions really well). I suppose if my battery is really shot the charger would indicate so. Nonetheless I'll invest in a battery sense for sure.
 

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The worst experience was at night time when the car lost all electric power after 2.5hrs long journey in heavy traffic, and when I was just about to park at the destination.... I anticipated this problem would recur and I even had the breakdown helpline number ready on my phone - but it was a smooth drive home
Are you saying the car died, and then, after parking it for an hour, it miraculously raised itself from the dead? If so, you don't have either a battery or a charging issue. You have a problem somewhere in the wiring or modules that is interrupting the flow of power from both the alternator and battery to the rest of the car. Have you tried scanning the car?

If you have the voltage monitor, and you have charging problam, the voltage will slowly reduce . Charging should indicate around 14 volts. Anything below about 12.8 indicates you're running primarily on the battery. Anything less than 12.6 means the battery is discharging.

At this point the cigarette lighter battery device arrived, so I plugged it in - read 12.1v. When I shifted seat position again it went down to 11.8 before reaching back to 12.1
Your readings sound a lot like mine, except I don't have your problem; my issue is the car goes dead from sitting. I believe trolls run the seat heaters at night while I'm asleep.
 

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Discussion Starter #46
Are you saying the car died, and then, after parking it for an hour, it miraculously raised itself from the dead? If so, you don't have either a battery or a charging issue. You have a problem somewhere in the wiring or modules that is interrupting the flow of power from both the alternator and battery to the rest of the car. Have you tried scanning the car?

If you have the voltage monitor, and you have charging problam, the voltage will slowly reduce . Charging should indicate around 14 volts. Anything below about 12.8 indicates you're running primarily on the battery. Anything less than 12.6 means the battery is discharging.
Yes the car miraculously raised itself from the dead! But the journey back was smooth and engine was at 2000rpm ish most of the time. I think the battery might have struggled to power all appliances in prolonged heavy traffic, but still had the ghost to start the car again.

When I tested the day before - with ignition on and engine idling - volt jumped very quickly to 14.5v.

Anyway, I also just found out there is another way to connect the charger to battery - via the fuse box under the hood! Not tried this yet - will give it a go next time - much easier than unscrewing the battery brace and taking off the plastic cover in the back/boot each time.
 

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Thank you so much for the really informative and helpful advice! I really, really appreciate it!

My car's battery is in the back so won't be able to test load without unlocking the car - unless I disconnect the negative after fully charged with a charger and see what readings I get after a day or two.

Earlier today I drove it to do grocery shopping - for the first time after the problem earlier this week (and after I cleared codes with VIDA) - battery was fully charged about 36hrs ago and the car started / drove with no issues - in heavy rain so headlights and all gadgets were on - it was a short trip to the supermarket after after reaching home I did a bunch of things with doors open and shifted seat positions for a good 20mins. At this point the cigarette lighter battery device arrived, so I plugged it in - read 12.1v. When I shifted seat position again it went down to 11.8 before reaching back to 12.1 again when I finished.

I'm going to buy a CTEK battery sense as recommended. My charger is CTEK 7000 (it's an old one made in Sweden and functions really well). I suppose if my battery is really shot the charger would indicate so. Nonetheless I'll invest in a battery sense for sure.
Early on you mentioned a new battery installation. I'm wondering what size it is?
I have a two year old genuine Volvo battery in my XC90 that was installed just before I bought the car. It's the little one, as compared by the mounting variations. I've putzed around with VIDA, programmed my Android radio, and listened to the radio while parked looking at the ocean. It's really not very long before the "Low Battery" message shows up with the key in position "I". It's a very pretty battery, but I work with deep-cycle battery systems on yachts, and know a puny undersized battery when I see one. If I wasn't so thrifty, I wouldn't wait until this battery goes Tango Uniform and replace it with the much larger AGM at Costco. Or whatever is a good deal ;)
One thing to consider is that car makers do anything they can to reduce the weight of cars to improve EPA MPG, and absent spare tires, puny batteries, plastic and aluminum panels, and air bolstered seats are all in the game.
 

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Discussion Starter #48
Early on you mentioned a new battery installation. I'm wondering what size it is?
I have a two year old genuine Volvo battery in my XC90 that was installed just before I bought the car. It's the little one, as compared by the mounting variations. I've putzed around with VIDA, programmed my Android radio, and listened to the radio while parked looking at the ocean. It's really not very long before the "Low Battery" message shows up with the key in position "I". It's a very pretty battery, but I work with deep-cycle battery systems on yachts, and know a puny undersized battery when I see one. If I wasn't so thrifty, I wouldn't wait until this battery goes Tango Uniform and replace it with the much larger AGM at Costco. Or whatever is a good deal ;)
One thing to consider is that car makers do anything they can to reduce the weight of cars to improve EPA MPG, and absent spare tires, puny batteries, plastic and aluminum panels, and air bolstered seats are all in the game.
This is the battery I put in about a year ago - EA1000 Exide Premium Car Battery 017TE

I watched a youtube video (
) where someone said XC90 can take a larger than stock battery - and that's what I did! Prior to this, I had a new Duracell regular size battery and was giving me 'low battery' a lot more often on cold winter mornings. Then it gave me x2 power outs during prolonged heavy traffic (admittedly they were about 1 year apart!) - that's when I decided to go for a larger battery
 

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Anyway, I also just found out there is another way to connect the charger to battery - via the fuse box under the hood! Not tried this yet - will give it a go next time - much easier than unscrewing the battery brace and taking off the plastic cover in the back/boot each time.
That’s where I connect all the time. Huge fat cable going from the engine bay jump start point back to the battery so no fear of voltage drop.

For the ground I click to the strut mount bolts


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That’s where I connect all the time. Huge fat cable going from the engine bay jump start point back to the battery so no fear of voltage drop.

For the ground I click to the strut mount bolts


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Now I understand what you meant by leaving the hood unlocked with rest of the car locked while charging overnight!

I just bought an used battery tester made by Midtronics - when it arrives it will be after Christmas and I shall give the battery a good test. I will probably charge overnight, then disconnect battery negative before testing.

I do believe the battery is OK - today after I played with the seat positioning for quite a while and the new cigarette volt reader gave 12.1v - I plugged in the charger for 1hr ish and it was up to 12.4v. The reason I had to stop the charger was it then began to rain again (and quite heavily soon after I disconnected the charger).

As I charge the car on the drive outside, I feel feeding the electricity cable through a gap in rear window, and charging the battery directly is a safer bet given the erratic British weather. I'm going to install wind deflector so the small gap would not let water in in heavy rain. I somehow fear by charging through the front fuse box there is a higher chance for residual rain water to get into the electronics in engine bay - I usually only open the bonnet when it is dry outside and there is no rain water left on the bonnet top. In contrast, the tailgate protects the battery much better as it extends back when opened - unlike the bonnet that goes straight up (if that makes sense)
 

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I think the battery might have struggled to power all appliances in prolonged heavy traffic, but still had the ghost to start the car again.
I think that's pretty unlikely. It takes an order of magnitude more current to start the car than it does to keep it running. I can't believe that it would recover that much with one hour's rest.

When I tested the day before - with ignition on and engine idling - volt jumped very quickly to 14.5v.
I'm wondering if it stays that high. I'd plug the volt meter in and go for a ride in heavy traffic and see what happens.

Anyway, I also just found out there is another way to connect the charger to battery - via the fuse box under the hood!
Yes, there's a jump point: a red box with a big "+" on it next to the fuse box. Use the ground point near the strut top for the negative connection. This is necessary because if you lock the tailgate there's no way to get to the battery without power to unlock it. You can route the power cord out around the side of the grill and close the hood.
 

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Yes, there's a jump point: a red box with a big "+" on it next to the fuse box. Use the ground point near the strut top for the negative connection.
Coincidentally I used this last night to jump another car. Turns out that + jump point isn't compatible with all jump cable clamps. The cables I used apparently were only designed to clamp at 90 deg, not from above the screw as is necessary with the tighter access in the XC90. Got it done but wasn't easy to get it securely clamped. That'll teach me not to charge my portable jumpstarter after every time I use it...
 

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As I charge the car on the drive outside, I feel feeding the electricity cable through a gap in rear window, and charging the battery directly is a safer bet given the erratic British weather. I'm going to install wind deflector so the small gap would not let water in in heavy rain. I somehow fear by charging through the front fuse box there is a higher chance for residual rain water to get into the electronics in engine bay - I usually only open the bonnet when it is dry outside and there is no rain water left on the bonnet top. In contrast, the tailgate protects the battery much better as it extends back when opened - unlike the bonnet that goes straight up (if that makes sense)
Once you have your charger connected lower the bonnet gentle without fully closing it. That’s what I do. The charger power cable exits the engine bay above the headlight, more than enough space for a cable


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Once you have your charger connected lower the bonnet gentle without fully closing it. That’s what I do. The charger power cable exits the engine bay above the headlight, more than enough space for a cable


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I've actually found a way to pass my (single gang) electricity socket end into the engine bay via a front grill hole - so able to complete close the bonnet while charging!
I still don't fancy charging via the front during rainy season - no matter how carefully I am each time I open the bonnet rain water just splashes down and I'm wary if it can interfere with charging if say water droplets lands on electric connections.

Also a quick update on my car's status, as I've been monitoring the battery and alt. via the cigarette lighter volt monitor:
  • last full charge by charger on Sunday.
  • when started on Monday noon, roughly 24hrs later, volt monitor read 12.2v
  • I started moving home with my car on Monday - about 15 miles each way, one round trip per day for Monday and Tuesday. Will continue to do so for the coming few days (only using removal company for really bulky items that won't fit into the XC90
  • the removal trips have been 'fully loaded' to the brim, and the car has managed well so far. When ignition was first switched on, volt monitor read 14.5v, which eventually stablished at around 13.4 (in traffic) to 13.8 (climbing uphill with engine at almost 3000 rpm)
  • I intend not to charge the battery with charger, while I drive it daily for about 1.5hrs (15miles return trip) for the next few days - well maybe not so on Christmas day... - and see how it copes
  • I hope to receive the battery tester I bought soon so I can give the battery a good load test
 

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Make note of the voltage reading after you first turn the key o, but before you start the engine. 12.2 is not eve close to fully charged, however, there is some evidence to suggest that the voltage reading at the lighter socket is lower than the actual battery voltage.
 

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Make note of the voltage reading after you first turn the key o, but before you start the engine. 12.2 is not eve close to fully charged, however, there is some evidence to suggest that the voltage reading at the lighter socket is lower than the actual battery voltage.
Yes the voltage at lighter socket will always be lower. There’s a very large load on the battery with ignition on and engine off. Voltage drop is normal. To know if the battery is fully charged you must measure under no load , which means car closed and locked for at least 2hrs
 

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A normal load should not draw a good battery down to 12.2 volts. I'm thinking the drop must be somewhere between the battery and the lighter socket. Easy way to tell is to compare readings at the battery and at the lighter socket at the same time.
 

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Discussion Starter #58
I’ve received battery tester today - after doing 3 trips of 15 miles each in variable traffic and in heavy rain sometimes with all wipers / fan etc on - I waited for 1hr after switching off the car and tested the battery - here are the results:

114696
114697
114698
 

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Just to satisfy my own curiosity - finally we have a clear night on Christmas Eve - so I plugged in the charger overnight and disconnected at 7am this morning. I then immediately disconnected the battery negative and left it like that for 6hrs. I tested again and the battery tester read 12.99v and 100 charged.

So pretty sure I can eliminate the bad battery possibility! I guess it’s now either down to alternator being quite old at almost 15 yrs and may struggle to cope with all electric applicants demand at low rpm when stuck in prolonged traffic - or there may be some kind of parasitic component in the car that draws battery amp when the car is not used?
 
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