Battery low warning

[rum4mo]

I've been checking up on my Erwin sourced (via easymanuals.co.uk) workshop manual for my wife's 2015 VW Polo and it says only to replace an EFB battery with an EFB battery, so that will be why any proper VW Group Indie toes that party line on that.

 

Battery manufacturers do suggest that swopping normal flooded with EFB is okay and swopping EFB with AGM is okay as long as you are able to provide the battery management system with the correct info - so I'd hope that any including Bosch will be able to supply all the info needed to feed into the battery management system fields.

 

I really do need to read up on this and examine the battery management system on my wife's Polo and log what all can and needs to get changed when a battery is replaced and especially when an AGM is going to replace an EFB.

 

I've just retested the battery in the Polo after finding that the advice is to give it a "bit of exercise" before testing it, ie switch ignition and main beams on for a few minutes - having full LED headlights might not give it much exercise, but I did that, retested the battery and the result was BATTERY GOOD - RECHARGE, 12.4V but the indicated CCA remained at 475A (EN) out of an original 640A (EN) the previous post RECON readings were REPLACE BATTERY 12.6V 475A (EN), so everything points to the 2015 Polo battery being past its best!

[FabiaGonzales]

FYI, you don't necessarily need VCDS to code in a new battery, most scan-tools should be able to do it.

 

Obd11 and Carista maybe too. Have a look at those before you splash a lot of cash!

[Confused_Cheese]

1 minute ago, FabiaGonzales said:

Obd11 and Carista maybe too

 

Odb eleven apparently can, Carista can't from what I've read. Depending on the type of module, it has to be coded differently 🤔 Some info here: 

 

 

TBH its all a bit out of my comfort zone, and with the car under extended warranty I might get Skoda to have a look. Any idea how many notes they'd be likely to relieve me of for a new battery 🙈

[Eccles]

I find all this techno overkill quite appalling and all for the sake of a few grams of CO2?  A couple of months ago my son's Picannto needed a new battery. I went and bought one from Halfords £65, bunged it in and off he goes, just as I have done many times in the past. It begins to look as though I will not be able to do similar for my Fabia 3 next year unless Gonzales knows different?

[FabiaGonzales]

3 minutes ago, Eccles said:

I find all this techno overkill quite appalling and all for the sake of a few grams of CO2?  A couple of months ago my son's Picannto needed a new battery. I went and bought one from Halfords £65, bunged it in and off he goes, just as I have done many times in the past. It begins to look as though I will not be able to do similar for my Fabia 3 next year unless Gonzales knows different?

I'd hazard a guess that if you have the battery current monitoring connector disconnected, you could run a standard battery in it. It might cause an issue at MOT time, so just plug it back in for the day, one day for testing isn't going to harm the battery.

 

Having the stop-start feature and all the regen charge features will rapidly kill a standard battery, that's why they need EFB or AGM batteries.

 

Basic explanation of how this works;
 

The little connector you disconnect is what's called a shunt resistor (typically fractions of Ohms). Used to measure current in and out of the battery.

 

Voltage = Current * Resistance,

 

Engine on will see a slight voltage drop across this shunt, perhaps 0.05v (dont quote me on this), and at 0.005 Ohm shunt, that means there is a 10Amp current going into the battery

When discharging, the voltage drop becomes -ve, resulting in a negative current reading, this may be as much as -0.5v, resulting in a reading of -100Amps (cranking the engine when cold for example) heading out of the engine.

 

Monitoring this at a high enough frequency lets the battery control module know how much charge the battery has lost and how much it needs to put in.
 

Stop-start works on a couple different parameters, the discharge current from the battery is less than a certain value, and the expected voltage drop of the battery when cranking is above a certain value. It also takes into account ambient temperature, but thats not too relevant here.

 

Disconnecting that shunt, the BCM cannot read the power going in and out of the battery at all and basically falls back to the old-style of charging the battery.

 

Disconnecting it also now means the resistance is infinitely high (air gap), so attempting to read a voltage drop across it will result in an infinitely high reading, and therefore an infinitely high current, this stops stop-start from activating hence it just shows up "high power consumption" or whatever on the reasons why it didnt turn off the engine.

[TerFar]

55 minutes ago, FabiaGonzales said:

I'd hazard a guess that if you have the battery current monitoring connector disconnected, you could run a standard battery in it. It might cause an issue at MOT time, so just plug it back in for the day, one day for testing isn't going to harm the battery.

 

Having the stop-start feature and all the regen charge features will rapidly kill a standard battery, that's why they need EFB or AGM batteries.

 

Basic explanation of how this works;
 

The little connector you disconnect is what's called a shunt resistor (typically fractions of Ohms). Used to measure current in and out of the battery.

 

Voltage = Current * Resistance,

 

Engine on will see a slight voltage drop across this shunt, perhaps 0.05v (dont quote me on this), and at 0.005 Ohm shunt, that means there is a 10Amp current going into the battery

When discharging, the voltage drop becomes -ve, resulting in a negative current reading, this may be as much as -0.5v, resulting in a reading of -100Amps (cranking the engine when cold for example) heading out of the engine.

 

Monitoring this at a high enough frequency lets the battery control module know how much charge the battery has lost and how much it needs to put in.
 

Stop-start works on a couple different parameters, the discharge current from the battery is less than a certain value, and the expected voltage drop of the battery when cranking is above a certain value. It also takes into account ambient temperature, but thats not too relevant here.

 

Disconnecting that shunt, the BCM cannot read the power going in and out of the battery at all and basically falls back to the old-style of charging the battery.

 

Disconnecting it also now means the resistance is infinitely high (air gap), so attempting to read a voltage drop across it will result in an infinitely high reading, and therefore an infinitely high current, this stops stop-start from activating hence it just shows up "high power consumption" or whatever on the reasons why it didnt turn off the engine.

This is how I operate. I disconnected the BCM from the battery terminal and ran perfectly for 9 months. I took the car for an MOT last week, so reconnected the BCM the day before taking into Skoda for year 4 service and MOT. When I collected it at the end of the day and drove it 1 mile home, guess what? Yes, that erroneous low battery warning came back. 

Skoda swear there is nothing wrong (charged me £60 to test the system). I swear the BCM is ****e! 

55 minutes ago, FabiaGonzales said:

 

 

[rum4mo]

Take care when talking to VW Group dealership workshop people as BCM is actually the Body Control Module which controls switching of power to consumers - battery management system is something else with either its own sub-controller or in some cases carried out within another controller, which for this segment car within the VW Group, I have yet to identify - could even end up being in the BCM!

[AGFalco]

https://www.golfmk7.com/forums/index.php?threads/how-to-retro-fit-a-bigger-capacity-battery-to-a-mk7-golf.320084/

 

Info here.

 

Thanks AG Falco

[Confused_Cheese]

Is the Mk7 golf the same platform in terms of coding as the fabia iii?

[Eccles]

Are you saying this great link is good for our Fabias as well AGF?

[Confused_Cheese]

Just done a 30 minute journey, start stop still wouldn't work at the end as high power consumption. I normally turn it off tbh so no idea how it normally behaves. Guessing that's not a great sign for the battery

[rum4mo]

What I was planning was either to just go for a size 027 AGM and use the VW Group part number 000 915 105CC if the battery management system does not like the Bosch part number. I messaged Tayna to ask if these Bosch S5 A05 batteries come with a BEM label and they replied that they do - or I go for the 096 size and look for a suitable VW Group part number for that one and swop the battery tray (console) for the Diesel one or modify the existing one to suit the extra length of the 096 size battery.

[BigEjit]

On 14/02/2020 at 16:06, FabiaGonzales said:

I'd hazard a guess that if you have the battery current monitoring connector disconnected, you could run a standard battery in it. It might cause an issue at MOT time, so just plug it back in for the day, one day for testing isn't going to harm the battery.

 

Having the stop-start feature and all the regen charge features will rapidly kill a standard battery, that's why they need EFB or AGM batteries.

 

Basic explanation of how this works;
 

The little connector you disconnect is what's called a shunt resistor (typically fractions of Ohms). Used to measure current in and out of the battery.

 

Voltage = Current * Resistance,

 

Engine on will see a slight voltage drop across this shunt, perhaps 0.05v (dont quote me on this), and at 0.005 Ohm shunt, that means there is a 10Amp current going into the battery

When discharging, the voltage drop becomes -ve, resulting in a negative current reading, this may be as much as -0.5v, resulting in a reading of -100Amps (cranking the engine when cold for example) heading out of the engine.

 

Monitoring this at a high enough frequency lets the battery control module know how much charge the battery has lost and how much it needs to put in.
 

Stop-start works on a couple different parameters, the discharge current from the battery is less than a certain value, and the expected voltage drop of the battery when cranking is above a certain value. It also takes into account ambient temperature, but thats not too relevant here.

 

Disconnecting that shunt, the BCM cannot read the power going in and out of the battery at all and basically falls back to the old-style of charging the battery.

 

Disconnecting it also now means the resistance is infinitely high (air gap), so attempting to read a voltage drop across it will result in an infinitely high reading, and therefore an infinitely high current, this stops stop-start from activating hence it just shows up "high power consumption" or whatever on the reasons why it didnt turn off the engine.

The downside to 100% charging an EFB or especially an AGM by disconnecting the minder is accelerated water loss reducing the life of the battery. The OEM charging cycle is set so it does not allow the battery to gas (boil) too much.

 

Gassing the battery during charging is when the water content of the electrolyte is being split into hydrogen and oxygen gas. Normally this recombines as condensate inside the battery and returns to the core, no harm done. Overcharging will cause more gassing and venting of excess pressure lowering the water content everso slightly each journey overcharging occurs. The longer it is left to charge uncontrollably, the more water content is lost.

 

Two things result.

The concentration or density of the electrolyte increases as the water content reduces causing faster decay of the lead plates. Decay causes loss of electrical storage capacity/ability to crank the engine. AGM has less water content to begin with than an EFB so this is more critical for these batteries.  

 

Overcharging accelerates the wear on the battery shortening the lifespan quickly.

 

Stop start batteries are designed to operate and last longer using intermittent charging cycles.

[Warrior193]

On 13/02/2020 at 22:21, FabiaGonzales said:

 

Some time a year or two ago, in a local Tesco car park, came by someone with another Fabia, their battery was shot, had to give them a jump start. Their battery was slightly bulged at the sides. Probably wouldn't have done bad to disconnect the battery after we'd started it up. It didn't look healthy. Don't know what ever came of it but yeah! (it worried me a little cos it was the same battery down to the same week of manufacture!) but mines still going as strong as ever. So far.

 

Warning - disconnecting the vehicle battery while the engine is running will very likely fry the alternator diodes due to the voltage "spike" 

[FabiaGonzales]

11 minutes ago, BigEjit said:

The downside to 100% charging an EFB or especially an AGM by disconnecting the minder is accelerated water loss reducing the life of the battery. The OEM charging cycle is set so it does not allow the battery to gas (boil) too much.

 

Gassing the battery during charging is when the water content of the electrolyte is being split into hydrogen and oxygen gas. Normally this recombines as condensate inside the battery and returns to the core, no harm done. Overcharging will cause more gassing and venting of excess pressure lowering the water content everso slightly each journey overcharging occurs. The longer it is left to charge uncontrollably, the more water content is lost.

 

Two things result.

The concentration or density of the electrolyte increases as the water content reduces causing faster decay of the lead plates. Decay causes loss of electrical storage capacity/ability to crank the engine. AGM has less water content to begin with than an EFB so this is more critical for these batteries.  

 

Overcharging accelerates the wear on the battery shortening the lifespan quickly.

 

Stop start batteries are designed to operate and last longer using intermittent charging cycles.

 

As far as i'm aware, AGM batteries are sealed. They don't vent, or shouldn't.

 

Running a standard flooded lead acid battery with the shunt disconnected is fine, those batteries prefer being fully charged and constantly trickle charged.

 

Gassing happens when the battery is charged too quick, like when regen-on-overrun occurs, pushing towards 15.6v into the battery.

 

I don't know enough about EFB and AGM to know their specific preferred charge currents and charge levels, but i don't see why the slow-medium charge rates without regen would cause any harm to them, when the battery gets full, the BMS should be able to see this and cut off charging.

 

Personally, i'd imagine it to be opposite to what you say, inside EFB and AGM there is much higher surface area between the electrolytes and the electrodes, this means at any one point on an electrode, the current, and therefore heat produced, will be less for the same total input / output current at the battery terminals.

This is why they are able to charge faster and provide higher output current too, for every given square mm of surface area between electrode and electrolyte, there is a limit to how much current can pass, increase the surface area, and you can have more current output.

 

Bigger batteries, more electrode and more electrolyte means more surface area resulting in more current and more capacity.

Same size battery, more surface area (EFB/AGM) means more current, but as the total amount of electrolyte and electrode remains the same, the capacity is unaltered.

 

[rum4mo]

21 hours ago, AGFalco said:

https://www.golfmk7.com/forums/index.php?threads/how-to-retro-fit-a-bigger-capacity-battery-to-a-mk7-golf.320084/

 

Info here.

 

Thanks AG Falco

 

Thanks for linking that info, saves me re-inventing the wheel!

 

All I need to do now is look and see which version of battery coding is in the 2015 6C Polo as it looks like the later version allows garages/owners to have more freedom from sticking with needing to use "VW Group only" batteries or use others if you can find a suitable equivalent VW Group part number.

 

I can't see me not moving up from a 027 case size to a 096 case size.

 

BTW, as I mentioned checking Coscto prices, Costco don't stock many AGM Bosch batteries but can get them in within a couple of days to order, I was given a price of £150 including VAT, but that price came from providing that car's reg number so maybe not even an AGM - I didn't clear that up as they were more than Tayna for either of the AGM Bosch batteries I was considering.

[Warrior193]

4 minutes ago, FabiaGonzales said:

 

As far as i'm aware, AGM batteries are sealed. They don't vent, or shouldn't.

 

Running a standard flooded lead acid battery with the shunt disconnected is fine, those batteries prefer being fully charged and constantly trickle charged.

 

Gassing happens when the battery is charged too quick, like when regen-on-overrun occurs, pushing towards 15.6v into the battery.

 

I don't know enough about EFB and AGM to know their specific preferred charge currents and charge levels, but i don't see why the slow-medium charge rates without regen would cause any harm to them, when the battery gets full, the BMS should be able to see this and cut off charging.

 

Personally, i'd imagine it to be opposite to what you say, inside EFB and AGM there is much higher surface area between the electrolytes and the electrodes, this means at any one point on an electrode, the current, and therefore heat produced, will be less for the same total input / output current at the battery terminals.

This is why they are able to charge faster and provide higher output current too, for every given square mm of surface area between electrode and electrolyte, there is a limit to how much current can pass, increase the surface area, and you can have more current output.

 

Bigger batteries, more electrode and more electrolyte means more surface area resulting in more current and more capacity.

Same size battery, more surface area (EFB/AGM) means more current, but as the total amount of electrolyte and electrode remains the same, the capacity is unaltered.

 

While AGM and EFB batteries are sealed in normal use, they WILL vent electrolyte if overcharged or otherwise abused - otherwise the battery casing could rupture due to excess pressure build-up.

[FabiaGonzales]

Just now, Warrior193 said:

While AGM and EFB batteries are sealed in normal use, they WILL vent electrolyte if overcharged or otherwise abused - otherwise the battery casing could rupture due to excess pressure build-up.

 

Just like SLA cells. Number of times seen old UPS (uninterruptible power supplies) for critical computer systems that have swolen and burst. Poor things just sit there being ever so slightly overcharged 24/7. It'd be better if they only charged them to 80% or so. Won't loose a great deal of run-time.

 

What do you think about using super-capacitors in parallel with a smaller, cheaper efb/agm or even standard battery?

Piggybacking them together with a decent supercap set can give you CCA test results as high as 2000 amps and even beyond.

Also prolongs the life of the battery, absorbing the huge spikes.

[BigEjit]

36 minutes ago, Warrior193 said:

While AGM and EFB batteries are sealed in normal use, they WILL vent electrolyte if overcharged or otherwise abused - otherwise the battery casing could rupture due to excess pressure build-up.

This 100%. There are vent channels in the lids of Lead acid batteries seen as a small hole on the end. 
 

AGM are also known as VRLA. Valve regulated lead acid referring to the pressure controlled gas valve installed in the lid labyrinth. 
 

Some vehicles already use super caps to support Stop Start systems so it is more than possible to do. 

Edited 15 February, 2020 by BigEjit

[lowedb]

I think that the unit that monitors battery current is the BEM (No not British Empire Medal). As someobody said BCM is Body Control Module, and on many VAG models there are BCM1 and BCM2. The BEM on the more complex versions is monitored by the gateway module, no idea if this is the case on this platform..

[Eccles]

....and on and on it goes. Hence I prefer KISS as we had in the old days (not that long ago actually). My son's eight year old Picanto does not have all this hitech/hicost unnecessary rubbish so the original battery did nearly seven years and was replaced by a £65 job from Halfords by me last year. I didn't have to tell the car it had a new battery, it just sort of knew it had one and started straight away. What the Dickens are VAG trying to prove? Next time I buy a car it will NOT have start/stop and it will not have keyless starting either.

[rum4mo]

11 hours ago, Eccles said:

....and on and on it goes. Hence I prefer KISS as we had in the old days (not that long ago actually). My son's eight year old Picanto does not have all this hitech/hicost unnecessary rubbish so the original battery did nearly seven years and was replaced by a £65 job from Halfords by me last year. I didn't have to tell the car it had a new battery, it just sort of knew it had one and started straight away. What the Dickens are VAG trying to prove? Next time I buy a car it will NOT have start/stop and it will not have keyless starting either.

 

Sounds like you will either be buying a very old car or an EV then, none of this is VAG trying to be clever, it is called progress/emissions reduction.

[TerFar]

1 hour ago, rum4mo said:

 

Sounds like you will either be buying a very old car or an EV then, none of this is VAG trying to be clever, it is called progress/emissions reduction.

 

So I really need a touch screen monitor covering half the dashboard because an old-fashioned speedometer and a couple of gauges use more fuel? How about windup windows, manual handbrake, manual dipping rear view mirror, etc: they all emit lower emissions? How about lane assist, park assist, cruise control, speed limiter: do they reduce emissions?

[rum4mo]

5 minutes ago, TerFar said:

 

So I really need a touch screen monitor covering half the dashboard because an old-fashioned speedometer and a couple of gauges use more fuel? How about windup windows, manual handbrake, manual dipping rear view mirror, etc: they all emit lower emissions? How about lane assist, park assist, cruise control, speed limiter: do they reduce emissions?

 

Go on, explain how that is connected with the comments that I was replying to ie, "Next time I buy a car it will NOT have start/stop and it will not have keyless starting either."

[J.R.]

33 minutes ago, TerFar said:

 

So I really need a touch screen monitor covering half the dashboard because an old-fashioned speedometer and a couple of gauges use more fuel? How about windup windows, manual handbrake, manual dipping rear view mirror, etc: they all emit lower emissions? How about lane assist, park assist, cruise control, speed limiter: do they reduce emissions?

All of these are just grooming drivers for when the next generation of vehicles will be self driving and not allow them to drive, by then they will be used to all these systems doing everything for them, newer drivers wont even have the skills or experience to do them themselves, all their journeys will have been spent staring into and swiping the touch screen monitor mirroring what is on their phone, by then the monitor will be the full width of the dashboard because there wont be that awkward and redundant steering wheel in the way of its expansion.