General Battery size confusion

[Pugglt Auld Jock]

Don't agree.
I had battery issues from the day I bought my 500 twinair, changed batteries, alternator, earth straps, negative battery terminals, and not once did the light come on on the dash. IMO, I think its solved now that I put another earth able on (link below), I've not had a peep out of it, regarding electrical issues.

Another Earth Cable

I think you're right, about when the ignition warning light extinguishes. It was always in the live feed to the alternator rotor windings in days gone by. when you switched the ignition on, current would be fed to the brush pack and thence to the slip rings and rotor windings (to establish a magnetic field) from there it went through a regulator and to earth. As the alternator revs increased so too did the output from the main windings which would oppose the current being fed to the rotor via the small connection on the alternator. As output from the main windings increased, because it was in opposition to the battery feed for the rotor a point was reached where there was insufficient differential between the two to light the little red light on the dashboard. In practice alternator output only had to rise to about 10 or 11 volts to reduce this to the point where the ignition light wouldn't illuminate. So, in "real life" the alternator could produce enough to cancel out the dashboard light but still not actually be charging the battery. I'm not entirely sure if this is so with "Smart" alternators where regulation/charging control is handled by a dedicated ECU?

Ralf comments above about the head lights light going dim and bright. This is an interesting one for "oldies" like me. Back in the days of dynamos they could not generate enough current at tick over to do much about providing a charge. So, one of the "classic" ways to check if charge was being applied to the battery was to switch the headlights on with the engine at idle RPM and observe headlight brightness against a wall or other suitable surface. - at tickover the system would be running at battery voltage of around 12.5 volts. Then lift the revs to a "fast idle" maybe 1500 to 2000 rpm whereupon the dynamo would provide charge and lift the battery voltage to 13.5, maybe 14.5 volts which would result in a noticeable brightening of the lights - job done, if the lights got brighter you could be pretty sure the dynamo was charging. Unfortunately this doesn't work so well now a days because alternators charge quite strongly even at idling rpm so revving the engine doesn't cause a rise in output sufficient to brighten the lights. Checking with a voltmeter is definitely the way to go on modern vehicles, especially as you can now buy a cheap but adequate multimeter for chicken feed. The Aldi/Lidl offerings are pretty good.

 

[GettinBetter]

I think you're right, about when the ignition warning light extinguishes. It was always in the live feed to the alternator rotor windings in days gone by. when you switched the ignition on, current would be fed to the brush pack and thence to the slip rings and rotor windings (to establish a magnetic field) from there it went through a regulator and to earth. As the alternator revs increased so too did the output from the main windings which would oppose the current being fed to the rotor via the small connection on the alternator. As output from the main windings increased, because it was in opposition to the battery feed for the rotor a point was reached where there was insufficient differential between the two to light the little red light on the dashboard. In practice alternator output only had to rise to about 10 or 11 volts to reduce this to the point where the ignition light wouldn't illuminate. So, in "real life" the alternator could produce enough to cancel out the dashboard light but still not actually be charging the battery. I'm not entirely sure if this is so with "Smart" alternators where regulation/charging control is handled by a dedicated ECU?

Ralf comments above about the head lights light going dim and bright. This is an interesting one for "oldies" like me. Back in the days of dynamos they could not generate enough current at tick over to do much about providing a charge. So, one of the "classic" ways to check if charge was being applied to the battery was to switch the headlights on with the engine at idle RPM and observe headlight brightness against a wall or other suitable surface. - at tickover the system would be running at battery voltage of around 12.5 volts. Then lift the revs to a "fast idle" maybe 1500 to 2000 rpm whereupon the dynamo would provide charge and lift the battery voltage to 13.5, maybe 14.5 volts which would result in a noticeable brightening of the lights - job done, if the lights got brighter you could be pretty sure the dynamo was charging. Unfortunately this doesn't work so well now a days because alternators charge quite strongly even at idling rpm so revving the engine doesn't cause a rise in output sufficient to brighten the lights. Checking with a voltmeter is definitely the way to go on modern vehicles, especially as you can now buy a cheap but adequate multimeter for chicken feed. The Aldi/Lidl offerings are pretty good.

Crap, I'm old enough to remember all that palava.
I'm warming to these intelligent alternators though, they don't put a single coulomb in if it doesn't need it. Hence don't put unnecessary wear and tear on all the parts involved, or waste fuel doing it. The voltage measured at the battery (engine running) stays at 12.7V come rain or shine, no matter what load I turn on.

 

[Ralf S.]

Don't agree.
I had battery issues from the day I bought my 500 twinair, changed batteries, alternator, earth straps, negative battery terminals, and not once did the light come on on the dash. IMO, I think its solved now that I put another earth able on (link below), I've not had a peep out of it, regarding electrical issues.

Another Earth Cable

That's fair enough.. but the discussion was veering towards "replace/upgrade the alternator". If the alternator is not charging because it's not working properly, then the charge light comes on. Yours was not charging because the battery wasn't earthed well enough, which is not specifically an alternator problem. That's what I meant..


Ralf S.

 

[Pugglt Auld Jock]

Crap, I'm old enough to remember all that palava.
I'm warming to these intelligent alternators though, they don't put a single coulomb in if it doesn't need it. Hence don't put unnecessary wear and tear on all the parts involved, or waste fuel doing it. The voltage measured at the battery (engine running) stays at 12.7V come rain or shine, no matter what load I turn on.

Yes, they are very clever aren't they. I try hard not to be too much of a dinosaur but the problem I have with a lot of this modern "tech" is that it's all very well when it's working as it should, saves fuel and is more efficient so contributes to saving the planet - but perhaps at increased manufacturing cost and greater use of "rare" materials? What's for sure is that it's going to be much more difficult to diagnose and expensive to sort when it goes wrong and there are much more parts which may go wrong - for instance free wheeling pulleys just for starters. However that can be an argument applied to many parts in modern vehicles. My point is that keeping a modern vehicle for as long as I've historically done (maybe 15 years on average, or until it's economically not worth repairing) is probably not now advisable. Buying after it's taken it's biggest price "hit" - is that still around 18 months to 2 years? - and keeping for possibly 5 years might be a better plan? What do you all think?

Just for illustration. We've just been down in Devon visiting Mrs J's elderly and rather frail sister. On the return journey, after our first comfort stop - at my age we need plenty of those - on restarting the engine and heading back onto the M5 I noticed the Infotainment screen had "taken a Benny". It was cycling through the startup boot and then immediately shutting down to a blank screen before, after a minute or so, repeating the process. It just kept on doing it. This is a touch screen so controlling many aspects of the car's function, not least of which being the Sat Nav. So I pulled into the next service area and switched off. Waited a few minutes and restarted, hoping this might "reset" it. Unfortunately it didn't so we just had to carry on with the screen repeatedly, and very annoyingly, trying to start itself. I eventually managed to ignore it, it's not as if I need the navigation help as I've been doing this journey for years. However, maybe some 20 minutes later, Mrs J said, "Oh look, the sat nav's working again!" From that moment on it continued to function normally for the next 7 maybe 8 hours until we got home. I've heard there are problems with VAG infotainment screens malfunctioning so, as the car is still under warranty, I'll be contacting the dealer about this. Probably just to get it logged as a fault with them during the warranty period as I think their reply will be that nothing can be done if no fault is being observed?

 

[Pugglt Auld Jock]

I should have mentioned above that Car Mechanics mag has a multipage write up all about alternators in this month's issue (May '25)

 

[Zardo]

0.9 TwinAir 65 HP 0.9 TwinAir 85 HP 1.2 petrol 1.4 petrol 1.3 MultiJet 75 HP 1.3 MultiJet 95 HP Voltage (V) 12 V 12 V 12 V 12 V 12 V 12 V Capacity / Intensity 63 Ah / 450 A* 63 Ah / 450* 40 Ah / 300 A® 50 Ah / 360 A© 63 Ah / 450 A* 40 Ah / 300 A® 50 Ah / 360 A© 63 Ah / 450 A* 50 Ah / 360 A 63 Ah / 450 A* 63 Ah / 450 A* (*) Stop/Start versions

They distinguish between with or without Start/Stop and with or without Xenon headlamps, the newer versions with S/S all have a S/S 63 Ah / 450 A battery. Also, S/S batteries need to be fully charged before installation/replacement, since the special voltage regulator apparently calibrates itself or something.

 

[Pugglt Auld Jock]

0.9 TwinAir 65 HP 0.9 TwinAir 85 HP 1.2 petrol 1.4 petrol 1.3 MultiJet 75 HP 1.3 MultiJet 95 HP Voltage (V) 12 V 12 V 12 V 12 V 12 V 12 V Capacity / Intensity 63 Ah / 450 A* 63 Ah / 450* 40 Ah / 300 A® 50 Ah / 360 A© 63 Ah / 450 A* 40 Ah / 300 A® 50 Ah / 360 A© 63 Ah / 450 A* 50 Ah / 360 A 63 Ah / 450 A* 63 Ah / 450 A* (*) Stop/Start versions

They distinguish between with or without Start/Stop and with or without Xenon headlamps, the newer versions with S/S all have a S/S 63 Ah / 450 A battery. Also, S/S batteries need to be fully charged before installation/replacement, since the special voltage regulator apparently calibrates itself or something.

Now that's a very interesting factor - that they need to be fully charged before installation. I've only been involved in replacing one stop start battery so far and that was the one on my Ibiza, which failed whilst we were on one of our Devon trips, so I just "bit the bullet" and handed it over to the local SEAT garage down there (together with a fair wad of the folding stuff) The VAG stuff needs coding with a dealer tool or something like VAG-COM/VCDS and you need to know the dedicated number/QR code on the new battery which you feed into the software. This, of course, very conveniently ties you into buying your battery from a VAG dealership! However I now believe you can do it by altering the number in the programming by a factor of just one digit - you still need VCDS or something similar to do it though and my interface is outdated for the latest cars so doesn't access many of the modules in later vehicles. However ensuring the new battery you're fitting is fully charged before introducing it to the system so the system programming starts off at the "right" point makes a lot of sense. Another thing I need to ask the VAG indy guys about.

We've only had one FIAT in the "family fleet" which was new enough to be Stop/Start and that was my oldest boy's 2012 Punto. It needed a new battery and I'd read on the forum that they self programmed (unlike the VAG stuff which has to be reset as mentioned above) so we bought a new Yuasa battery for it from the ever helpful Frank at Seafield Halfords and just fitted it in their car park - didn't think about checking it's state of charge. I guess it must have been ok though because the stop start worked from the moment he drove out of the car park and continued to work until the car was written off by that "death wish" lane changer outside the Royal Commonwealth Pool.

 

[Zardo]

Now that's a very interesting factor - that they need to be fully charged before installation.

yeah, but only for S/S or Euro 6 apparently, and > 80%.
Older batteries may drop quickly below that if the car isn't driven regularly.

After removing and refitting the battery monitoring sensor it is necessary to check that the battery charge is not less than 80%. Otherwise, recharge the battery so that it is more than 80% charged. If the battery is being replaced, check that the replacement part is a Heavy Duty version approved for Start&Stop.