14 minutes ago, Wino said:

 

Are you sure it isn't the other way round?

 

This paragraph from batteryuniversity.com page on the subject suggests to me that it is the AGM type that would be vulnerable to damage if fitted in a car with conventional charging:

 

"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive."

 

 

A standard battery doesn't like the higher currents and voltages that the regenerative braking provides,

 

EFB and AGM batteries don't like the constant charge voltage that a standard system provides.

 

Ideally you should replace the battery with whatever type came with from factory.

 

Nowadays it's generally safe to upgrade the types via coding the BMS (battery management system) which alters max charging currents and float voltages accordingly for the battery type installed, while going backward is also doable by the same methods, you're putting extra stress on a battery that wasn't designed for such activities.

 

My factory installed EFB battery's going on toward 6 years of service now, not missed a beat. Why you want to replace a standard battery multiple times when a properly looked after correctly matched battery may not need replacing at all during the time you own the car?

 

There are a lot more metrics to look at other than "engine starts" when it comes to car batteries. Standard cells don't like the deeper charge cycles that stop/start involves, for example, they prefer to be fully charged all the time, but stop/start is rarely going to allow that kind of condition. AGM doesn't like being sat on charge all the time when it's full, like when installed in a non stop/start car, rather they prefer the constant charge cycling of a stop-start system.

Where's your info source for your first sentence, please?

17 minutes ago, Wino said:

Where's your info source for your first sentence, please?

It's difficult to find useful into, but EFB (and AGM) have considerably higher charge current acceptance than standard batteries.

 

Here's one source;

https://www.yuasa.co.uk/info/technical/agm-efb-explained/

 

Standard cells have limited electrode surface area due to their design (efb and agm fix that) and a battery can generally only accept so much current per the surface area at a given charge voltage.

 

Depending on how the BMS is set up, it may keep the voltage low on regeneration (and therefore the current will be low too), in which case the battery will struggle to get charged up sufficiently before the next stop/start event, and will slowly become deeper discharged over time and fail quickly (standard batteries dont like low charge states, they sulphate), or it might try to push the same current as it would do for an efb or agm battery, it would do that by ramping up the voltage considerably which as we know can overheat and damage the battery by effectively boiling the acid off.

 

With agm due to their design with lower internal resistance than standard cells they will pull more charge current at a given float voltage, that's why they need a lower float voltage, else they sit there sucking up all that current and overheat. It's easier to simply hold the battery at a lower state of charge (usually 80-90%) as the battery is still able to put out plenty of power, that charge level is fine for an agm battery and it also stays away from any overcharging.

Higher 'charge acceptance' and lower internal resistance seem like different ways of saying the same thing, probably. So your standard battery will simply not be subjected to as a high a charge current for a given alternator output voltage.  And surely it's the charging current that causes overheating/boil-off if it's too high, not the voltage? 

 

From logs I've seen on this forum, the high-voltage (not that high in those logs, only 14.8V or so) spikes are very brief anyway (as you'd expect from their necessarily (usually) brief causation, braking/overrun conditions.) I suppose significant hill descents could produce longer high-voltage 'spikes' but may well be software time-limited anyway.

Anyone reading monitor their system voltage while descending long hills?

 

 

15 minutes ago, FabiaGonzales said:

It's difficult to find useful into

Which is one reason I doubt the truth of it.

Another is that if you read that battery university page without due care and attention, you can get it backwards from there; it's not phrased very clearly.  Could it just be people misquoting that page, creating an 'internet rumour'?

 

 

 

 

9 minutes ago, Wino said:

And surely it's the charging current that causes overheating/boil-off if it's too high, not the voltage? 

 

Yes, but it would depend on how the BSM handles the overrun charging.

 

If it's designed to throw (for example, actual charging currents and voltages would be much lower) 100 amps at 15v at an EFB battery,

A standard battery being given that voltage, would only soak up approx 50 amps or so due to its higher internal resistance, the BMS might try and compensate by increasing the voltage (to say, 16v), and the current would rise somewhat accordingly.

 

The heat generated by charging is dependant upon the internal resistance and the current being accepted.

This theoretical EFB battery has 0.15 Ohms internal resistance, and the theoretical standard battery has 0.30 Ohms internal resistance.

 

The EFB battery would be seeing 0.15 Ohms * 100 amps, so it would see 1500 watts of power going into the battery. Because the internal surface area is much larger, this doesn't really pose an issue.

The standard battery would be seeing 0.30 Ohms * 50 amps, so again it would see 750 watts of power going into the battery. No issues there yet, the lower surface area means it can accept less power.

The standard battery being forced a higher charging rate (if the BMS were to try such a thing, perhaps to try compensate for the fact the battery isn't charging up enough between stop/start events), that increase to 16v charge voltage would only net 53 amps charging current, but it's now sucking in 853 watts.

 

The overcharged standard battery just isn't going to last as long, it's going to get considerably hotter than it's designed to and it will slowly boil off the acid over time, futher reducing surface area and accelerating the issue till it's dead.

 

Obviously real life values will be considerably lower, as internal resistances are nowhere near that low, but you get the idea.

 

It's like a 100w light bulb vs a 50w light bulb, you can make a 50w bulb output the same amount of light as the 100w one by increasing the voltage (and therefore current), but that small fillament is going to melt very quickly.

10 minutes ago, FabiaGonzales said:

BMS might try and compensate

The logs I saw (and am desperately trying to remember in which thread) showed voltage and current. The voltage spikes were always of similar magnitude, and the current spiked high in response but rapidly decayed down while the voltage was still at that value, IIRC, suggesting that it was voltage that was being controlled, with current just doing Ohm's lawy stuff as the load impedance changed.

If the BMS were actively trying to coerce some given current from the alt, these things would be the other way round, I think? (Current would go up and stay at a fixed value while the voltage danced around as required to maintain it there).

 

 

15 minutes ago, Wino said:

The logs I saw (and am desperately trying to remember in which thread) showed voltage and current. The voltage spikes were always of similar magnitude, and the current spiked high in response but rapidly decayed down while the voltage was still at that value, IIRC, suggesting that it was voltage that was being controlled, with current just doing Ohm's lawy stuff as the load impedance changed.

If the BMS were actively trying to coerce some given current from the alt, these things would be the other way round, I think? (Current would go up and stay at a fixed value while the voltage danced around as required to maintain it there).

 

 

Then that's how our BMS handles it, so it shouldn't overcharge on overrun.

 

That still leaves the main issue with the fact that as standard batteries have higher internal resistance, they won't be able to take on as much charge from regenerative braking and overrun, that'll leave the battery in a constantly low state of charge that's going to encourage the formation of sulphur crystals on the electrodes.

 

EFB and AGM batteries don't have such issues by design, but they don't like being constantly charged (standard ones like being trickle charged, agm prefer a pulse maintenance style of charging).

5 minutes ago, FabiaGonzales said:

that'll leave the battery in a constantly low state of charge

It's going to seem like I'm constantly disagreeing with you for the sake of it, but that's not true.

 

The BMS will increase the background charging voltage if it 'feels the need to'.  I think there was evidence of this in some of the logs mentioned.

 

Imagine an open country drive on an empty freeway where you might potentially go for hours and hours without needing to brake, or descend a hill, just plodding away. Australia, US etc.  Is the battery management going to still rely on recuperative charging, and just let the battery run down until you stop? Doesn't seem likely. 

 

Can anyone remember the thread I'm thinking of.  Aussie guy with a username something like bobsuew, maybe in an Octavia or Superb subforum?

2 minutes ago, Wino said:

It's going to seem like I'm constantly disagreeing with you for the sake of it, but that's not true.

 

The BMS will increase the background charging voltage if it 'feels the need to'.  I think there was evidence of this in some of the logs mentioned.

 

Imagine an open country drive on an empty freeway where you might potentially go for hours and hours without needing to brake, or descend a hill, just plodding away. Australia, US etc.  Is the battery management going to still rely on recuperative charging, and just let the battery run down until you stop? Doesn't seem likely. 

 

Can anyone remember the thread I'm thinking of.  Aussie guy with a username something like bobsuew, maybe in an Octavia or Superb subforum?

True, the BMS does use a standard charging scheme to get the battery up to somewhere around 80% or so, after that it drops off to basically the battery doing nothing and the alternator is powering all the car functions. But still standard batteries aren't too fond of being even that low, they prefer being full all the time and being trickled constantly.

Yep, I would disco the LIN connection of the BMS if I fitted a non-suitable battery to a start/stop car, I think, or even put a switch in it so I could selectively 'undisable' start/stop if I chose to. That should make the alt default to traditional fixed voltage charging.

Ah, I found the post with the logs; it was @Andysuew not bobsuew!  

 

Those logs are with start/stop switched off, but the system not nobbled.

 

 

Just an additional note on why standard SLI flooded batteries are not advised for stop start systems factory fitted with EFB/AGM.

 

They will work but they can't handle the cyclic loading as well as EFB/AGM. They are not intended for the aggressive deep discharge and recharging Stop/Start profiles operate under (both with and without engine cut function selected) unlike EFB and AGM. They wear out quicker and need replacing way sooner as the lead paste and grids decay and turn to mush in the bottom of the container from the batterings. SLI will deep discharge cycle 200 or 300 times compared to AGM 500 to 600 times with equivalent test strategies before they are done (targeted for 10 year life expectancy).

 

A one second engine start doesn't impact the battery that much (250 seconds is typical minimum available discharging time to 6v), Its how the energy distribution is managed during the rest of the time with consumer items and charge requests kicking in and out constantly that is more critical.

 

 

8 hours ago, BigEjit said:

Just an additional note on why standard SLI flooded batteries are not advised for stop start systems factory fitted with EFB/AGM.

 

They will work but they can't handle the cyclic loading as well as EFB/AGM. They are not intended for the aggressive deep discharge and recharging Stop/Start profiles operate under (both with and without engine cut function selected) unlike EFB and AGM. They wear out quicker and need replacing way sooner as the lead paste and grids decay and turn to mush in the bottom of the container from the batterings. SLI will deep discharge cycle 200 or 300 times compared to AGM 500 to 600 times with equivalent test strategies before they are done (targeted for 10 year life expectancy).

 

A one second engine start doesn't impact the battery that much (250 seconds is typical minimum available discharging time to 6v), Its how the energy distribution is managed during the rest of the time with consumer items and charge requests kicking in and out constantly that is more critical.

 

 

 

Thanks and interesting.  If I could have got a EFB/AGM for less than £100 I might have gone for it. Living in suburbia and usually driving out toward the countryside or motorway I do think the start stop would be used other than every few kilometers so well within the 20,000 restarts a standard battery will do and probably 5 minutes at least between require restart in country roads and not at all on motorways where the diesel is really at home and on country roads I would think about taking the turbo petrol Clio which seems to match the diesel for fuel consumption on those shorter journeys.

 

I have seen prices of £200, £300 and even £400 for AGM batteries and often they are only 70 AH or less.

 

I see a disturbing lack of evidence of AGM is terms of their recharge rate compared to conventional batteries.  I have that simply formula that conventional lead acids are OK charging at 10% Amps rate ie 80 AH battery can handle and will absorb 8A at 14.5V ie say 115 joules per second and probably retain about 100 joules and the rest is heat wastage.

 

So will an AGM accept 12A, 16A, 20 A if available from that oversized heavy duty alternator which one will have fitted with the start stop system ?  Where is the comparison data ?

 

If the standard battery only lasts 3 years then I would hope to be able to switch to Lithium 

 

Get the Lead out......

 

 

  

The prices quoted by "your fav cheap place - not" ECP, for a Bosch AGM for my 2011 S4 was "only" roughly £540 - but again "only" £325ish with "never to be repeated (until next month)" discount - Costco, luckily had a December discount on their Bosch car batteries, so I got one for £153 - which was okay!

 

That was a Bosch 019 case size S5 95Ahr 850A CCA.

Edited 27 March, 20215 yr by rum4mo

With car batteries, bigger isnt necessarily better

 

Neither is AGM vs EFB

 

Recharging to 100% often and regularly is key to maintaining all lead acid batteries  in prime condition, thereby stopping permanent and irreversible hard sulphation forming and slowly losing capacity.

 

A decent charger is one that does a proper float/maintenance mode after bulk/absorption charging, at a constant 13.5 volts + temp comp. IME it takes 2+ days continuous charging to top off the final 5-10%.

 

Tanya is worth a look for batteries

 

Yup, I think that my CTEKs end up in maintenance mode after 7 days, and so just jab the battery with charge after it has dropped back down to 12.7V back up to 13.2/13.4V - my own car frequently ends up at that stage!

 

Costco only beat Tayna because of Costco's December battery "event" - that combined with Brexit maybe causing prices to rise along with initial supply replenishment issues when UK opens up again, and the original battery being 10 years old all combined for me to grab a new one.

 

Edit:- on the topic "bigger isn't necessary better" hopefully most people that work on their cars realise that "bigger and cheaper" over time is not necessary better than "same size and same brand as fitted at factory" - just how good is a long warranty on a cheap battery when you are immobile many miles from a branch of that vendor, better to always put the money into the product and not the warranty.

Edited 28 March, 20215 yr by rum4mo

So, recently my top right engine mount (the one next to the coolant reservoir) split (and made a right mess), I ended up swapping all 3 engine mounts for Polo GTI ones.

 

Anyway, to do this i had to remove the battery (albeit only temporarily). I disconnected the +ve first, and connected it up last.

 

Stop-Start was working properly beforehand, but since the mounts have been replaced, stop-start no longer works, it simply states "engine must be running", i've a bluetooth OBD module which shows the battery gets to ~85% charge via flat rate 14.8v, once it hits that point it drops to overrun-only charging.

 

Still no stop-start though. Any clues?

The only time I've had that was when the VW dealership accidentally left unplugged, the BMS lead at the -VE battery post.

 

Is that cable still okay and plugged in?

1 hour ago, rum4mo said:

The only time I've had that was when the VW dealership accidentally left unplugged, the BMS lead at the -VE battery post.

 

Is that cable still okay and plugged in?

Yeah i've checked that.

 

If i unplug that, the charge % reading doesnt work and voltage sits at a steady 13.8 ish, no fluctuation for overun or anything.

 

Might disconnect it and reconnect it again to see if that changes anything.

21 hours ago, FabiaGonzales said:

I disconnected the +ve first, and connected it up last.

 

8 hours ago, FabiaGonzales said:

Might disconnect it and reconnect it again

Negative first, positive second on disconnect and the other way when reconnecting, please.

 

Thanks AG Falco

 

Maybe some coding has changed with the battery being disconnected, it should not have, but I've read about people finding the odd change in things after a battery has been disconnected.

 

A bit of sniffing around with VCDS would prove if stop/start is still coded in.

3 hours ago, AGFalco said:

 

Negative first, positive second on disconnect and the other way when reconnecting, please.

 

Thanks AG Falco

 

I disconnected & reconnected it like that (same as in the user manual), no change.

 

3 hours ago, rum4mo said:

Maybe some coding has changed with the battery being disconnected, it should not have, but I've read about people finding the odd change in things after a battery has been disconnected.

 

A bit of sniffing around with VCDS would prove if stop/start is still coded in.

 

I don't see anything that's changed, or at least i didn't see anything different before i started poking.. 😂 I was curious to see whether changing the battery serial would have any effect (to make the BMS see it as a "new" battery)

 

type was set to efb (i left that alone)

manufacturer was set to JCB (eh? I left that alone too)

serial was 1111111111 (which i just zeroed out)

 

The result? charging voltage dropped to about 14.4v, and now once it hits 75% ish, it drops to 13.3v ish (previous 13.6v ish) unless on overrun.

 

No return of stop/start yet.

 

The battery has been disconnected before (and as far as i can remember, stop start worked again straight after).

 

Recently after being a little deeper drained a few times (when having the hybrid turbo tuned in sat with ignition on engine off etc), it's taken a few days to recover and resume stop/start functionality.

 

The other wierd little thing it does is when lifting the clutch (in neutral) it raises revs as if it expects me to pull away. It's done that previously when "recovering" too but it's a little random thing ive noticed

 

I've ordered a Yuasa YBX9027 AGM battery. Whenever that comes i'll code that in properly with the actual serial and manufacturer code (does anyone know the manufacturer names-codes references?) and see how i get on with that. I have a feeling this battery is on its way out. Even with a good 1hr+ drive out, shutting off and leaving for 12hr the battery is usually sitting around 11.8v ish and it drops to 9v (and possibly lower) the cars not complaining about it or anything, just stop/start not functioning.

 

Edit: previously it only used to drop to ~10.5v when starting the car (and even after prolonged cranking by disconnecting fuel pump it stayed above 10v)

Edited 7 April, 20215 yr by FabiaGonzales

11 hours ago, FabiaGonzales said:

I disconnected & reconnected it like that (same as in the user manual), no change.

 

 

I don't see anything that's changed, or at least i didn't see anything different before i started poking.. 😂 I was curious to see whether changing the battery serial would have any effect (to make the BMS see it as a "new" battery)

 

type was set to efb (i left that alone)

manufacturer was set to JCB (eh? I left that alone too)

serial was 1111111111 (which i just zeroed out)

 

The result? charging voltage dropped to about 14.4v, and now once it hits 75% ish, it drops to 13.3v ish (previous 13.6v ish) unless on overrun.

 

No return of stop/start yet.

 

The battery has been disconnected before (and as far as i can remember, stop start worked again straight after).

 

Recently after being a little deeper drained a few times (when having the hybrid turbo tuned in sat with ignition on engine off etc), it's taken a few days to recover and resume stop/start functionality.

 

The other wierd little thing it does is when lifting the clutch (in neutral) it raises revs as if it expects me to pull away. It's done that previously when "recovering" too but it's a little random thing ive noticed

 

I've ordered a Yuasa YBX9027 AGM battery. Whenever that comes i'll code that in properly with the actual serial and manufacturer code (does anyone know the manufacturer names-codes references?) and see how i get on with that. I have a feeling this battery is on its way out. Even with a good 1hr+ drive out, shutting off and leaving for 12hr the battery is usually sitting around 11.8v ish and it drops to 9v (and possibly lower) the cars not complaining about it or anything, just stop/start not functioning.

 

Edit: previously it only used to drop to ~10.5v when starting the car (and even after prolonged cranking by disconnecting fuel pump it stayed above 10v)

 

 

I think those Symptons of the start stop not working even after a 100km highway drive that I have are the same as your with teh original EFB. Yours was also a 2015 EFB Moll right? mine died this winter where it was competely dead(needed to open with the key not even remote worked). Before it was compeltely dead, the voltage before starting was around 10.8 V, but the car always started fine.

My experience with the AGM (A Varta in my case, quite cheap just 90 euros) is very good, I just changed to fleece with the OBD like it was clarified in the forum, and just like you showed there. :-)

I think at least in Europe, "JCB" is just the default manufacturer, ie Skoda did not recode with the actual battery that the car was to be fitted with, VW also don't seem to always change the manufacturer in the BMS settings - and yes 11111111111 is also just the default for serial number.

 

I'm not sure what the Yuasa code is, but their vendor should be able to tell you, though again I'm not sure if it is critical, could be wrong there though.

On 26/03/2021 at 07:50, lol-lol said:

 

Thanks and interesting.  If I could have got a EFB/AGM for less than £100 I might have gone for it. Living in suburbia and usually driving out toward the countryside or motorway I do think the start stop would be used other than every few kilometers so well within the 20,000 restarts a standard battery will do and probably 5 minutes at least between require restart in country roads and not at all on motorways where the diesel is really at home and on country roads I would think about taking the turbo petrol Clio which seems to match the diesel for fuel consumption on those shorter journeys.

 

I have seen prices of £200, £300 and even £400 for AGM batteries and often they are only 70 AH or less.

 

 

 

 

 

It didn't take me long to find a suitable EFB battery for £85, free postage on ebay last year and my wonderful mobile mechanic fixed up the BMS with his electronic device (don't know what they are called) for a fiver. So yah boo sucks to main dealers and Halfords.