The main battery is the one to look at. The secondary battery is only connected to the car by a relay for a fraction of a second during an engine restart from a stop/start event, when it momentarily takes the load of running consumers, to free the main battery capacity entirely to service the operation of the starter motor.

 

Perfect, thanks. Will it let me know if I ever need to change the secondary battery? Or is it recommended to replace it after a certain amount of time?

 

I don't think any message will appear in the cluster. It may cause a fault code if it fails and can also be diagnosed with Vida, but unless you are particularly bothered about having to have start/stop working, it won't cause any other issues. Replying as someone who has disabled start stop on both my V40 and my wife's Kia, you might even see that as a desirable consequence

 

Start/stop hasn't worked for a few years now, but I never liked it (and I don't know anyone who does) since it must surely cause the starter motor to fail sooner. It just seems awkward in traffic, anyway, and I always have a nagging worry that it won't start again when required. I didn't know you could disable it permanently, though? I'm certainly interested in doing that, if a new battery makes it start working again. I never knew why it stopped working, and in the last couple of days, while thinking about the low battery warning, have come to assume that that has been the cause all along.

 

The low battery message is fairly common and in itself not necessarily an indication of a bad battery. You will find more in-depth descriptions in various posts if you search the group for that message, but basically the car keeps the main battery at around 85% SOC to allow headroom to accept alternator charging between stop/start events. There is therefore much less headroom than on a traditional charging system for the battery to power the radio etc. when the engine is off, because the battery by design is rarely if ever fully charged. The system also calculates the average quiescent current draw continuously, and that value can increase also if you use the radio with the engine off, which in turn affects how much time the system thinks is left before the battery will reach the low charge floor, and so the message can be generated prematurely.

But a genuinely bad battery is more likely to be a cause of various other errors and fault codes as well, so worth fitting a new battery if there is any doubt about the existing one. The Battery Management System has to be reset when a new battery is fitted, which amongst other things, resets the quiescent current drain to a default and low figure. That can be done with diagnostic equipment which has that capability, or by a sequence of button presses in the car. Again details on the latter method can be found in other posts, or someone who has used it may reply. As I have suitable diagnostic equipment, I've never bothered to learn the button press method.

If the new battery isn't exactly identical in capacity etc. to the old one, the relevant information should also be programmed into the car.

To disable start/stop, on my V40 I used VDash to reprogram it to work in reverse, so it's always disabled when the car is started, but can be enabled by pressing the button in the console. It can also be disabled completely if preferred. On my wife's Kia I just inserted a small piece of plastic down the side of the start/stop button to keep it depressed all the time. That may also work on the V40 and would be cheaper.

 

Many thanks for that interesting and comprehensive post. I should be getting a (Yuasa) battery delivered today; but since it looks like a more complicated job than one might expect, I may need to wait until tomorrow to fit it. I'm hoping my Foxwell can do the reset - it claims that it can in the blurb that came with it.

The VDash thing looks interesting. I have a selection of OBD connectors and cables that might partially work with it, but I expect I'm going to have to get another one for the collection.

 

When my second battery was going faulty the stop start and city safety was ‘unavailable low battery charge’ then the following days my car kept shooting random warning lights constantly all day as I got to garage the car cut out and wouldn’t start at all until I changed battery

 

Hm. I wouldn't want that to happen at all. Like I say, this is the missus' car, and having it cut out away from home is something she would react pretty badly to. My own car is a very humble and predictable Fiesta that I've managed (with a bit of work, of course) to keep going for 22 years. I know one shouldn't, but I've grown attached to it. The Volvo is a whole other level of complication that I'm not completely comfortable with.

I may have to find a way to test the secondary battery. On the other hand, if I can disable Stop/Start, it might help avoid such problems. On the third hand, any battery, used or not, will deteriorate anyway.

 

Ours hasn't been so bad, except that both front springs broke within a few years of us getting it, which was quite dangerous, since both left sharp edges digging into the tyres, which fortunately we heard before it could actually rip them open. In fact one was broken when we bought it. I thought it was making more noise than you would expect when you went over a bump, and when I looked at it, the spring was broken, and the two pieces were banging about against each other. The other side spring broke a few years later. I assume it was a bad batch, because I changed them (since I already had experience with a spring compressor), and haven't had a problem with them since. Also, one of the front calipers seized on, which was fun too. I know that things go wrong with cars, but the missus was a bit miffed because she associates Volvo with safety, and things that are not supposed to go wrong. I tell her it's just another car.

The complications of all modern cars annoys me, though. I am reminded of a quote by Douglas Adams: The problem with things that can't possibly go wrong, is that when they do go wrong, they are impossible to fix.

 

Just get rid of it while you can, it’s a piece of **** car the v40 it’s a financial burden I spent too much money keeping it running. Looking at buying Audi soon or skoda superb

 

To date I’ve replaced rear shocks, front control arms, ball joints, bushings, front springs, front shocks, clutch lines, clutch, clutch pedal, master clutch cylinder twice, brake booster pressure sensor and that’s all I can remember. The car is a piece of **** I hate it 😂

 

Okay, pro tip: get a genuine Volvo branded battery from a main dealer. They come with a five-year warranty, and no one has ever returned one under warranty.

I replaced the battery on mine, and it was a pain. I had to remove the torsion bar. Then there was an in-line fuse which fell out and ended up in the pan underneath the engine.

 

Okay, I finally fixed my original error. I changed the battery so the Low Battery message went away. It didn't fix the ABS/DSTC message (I wasn't really expecting it to, but you never know), but I used my scanner to show individual wheel speeds which showed that the rear right wheel was stuck at zero. I changed the sensor today and after a short drive round the block (a couple of hundred yards with some left and right turns) the ABS/DSTC message disappeared (and start/stop works again, which I'll try to turn off); but then a City Safety message appeared. After clearing a few historic fault codes (which I think I'll blame on the old battery), that went away, and now all is good. Interesting that the ABS error can't be cleared by my scanner, but goes away when the car has decided it's okay. I suppose that makes sense.

 

I believe the car does a check when it reaches 14kmh for the abs errors