This is something I'd read...

80% charge apples to pure BEV. PHEV cars like GTE have massive battery buffer of 30% which is like 15% top and bottom so there should be no problem to charge it to 100% or keep it discharged for long time. This large buffer is done for the reason that PHEV can very often stay at 0% for a long time, and also be plugged on for long time. This scenario is not the same for BEV, where you usually do not go bellow 10% often. Also buffers of the battery are smaller for pure BEVs. So in my opinion keep it charged to 100% for PHEV should not be a significant risk for the high voltage battery...

 

Seems odd for a PHEV as these are designed to be fully charged and discharged at least once a day.
I see @Mookistar has provided the answer.

As a side note if the wall reports 14.98 kWh going into the car then the actual amount going to the battery after charging losses will be around 13kWh, expect 10 to 20% charging loss, Granny leads will have the higher loss, wall boxes lower.

 

With my previous Mk8 GTE I always fully charged it and happily let it go to zero miles. With my Mk8.5 VW encourages charging to 80% and when the range shows anything below about 5 miles in the App the figures are in red.

Regarding power losses with 10.9 kWh useable battery (13 kWh in total) on my Mk8 according the Octopus App it never exceeded 11.0 to charge.

 

I wonder if they’re just using the same UI as the full electric models. No reason it should be any different but no doubt VW will use it against you in event of a battery claim.

 

With the Mk8 it is well known that the size of drive battery is 13 kWh, usable 10.9 kWh. I have not been able to get any information on the usable capacity of the Mk8.5. If, like you say Moonistar, it shares the UI with VW’s BEVs why have they not included the ability to set the minimum charge to 20% or perhaps 10%?
And don’t getting me going on the fact that the chargers timer has been removed from the Mk8.5 🤬.

 

This sounds like absolute nonsense to me. You can't be expected to nurse a PHEV battery like that.


What does the handbook say?

 

Batteries in HEVs or PHEVs are designed for a large number of cycles, considering they have smaller capacity. For example, over 200.000 km they must perform a larger number of cycles than the batteries in a BEV (50-90kWh avg). Depending on the model, they use a optimal charging range (20 - 80 or 30% - 70%) , although charging and discharging rarely exceed 0.5C or 1C, only occasionally (up to 5 seconds) can go beyond 1C.

 

Two observations from the following that I found in the digital manual for my GTE.
1. ‘Avoid complete discharge’. This is unavoidable with a PHEV. On all longer journeys it’s inevitable that the of battery will be depleted by journeys end and there is no way to stop this happening.
2. There is no ‘Timer-controlled charging’ (another topic).

Charging instructions

• For everyday use, set the upper battery charge limit to 80% in the Infotainment system Battery charge limits or activate Battery Care Mode.
• Do not charge the high-voltage battery after every journey if only a short distance has been driven in purely electric mode, but charge only when necessary.
• Plan charging processes for a later departure time with the departure times in the Infotainment system Timer-controlled charging. At low ambient temperatures, this optimises the temperature of the high-voltage battery and improves performance.
• Charge the high-voltage battery when the charge level is below 20%. Avoid complete discharge of the high-voltage battery if possible →
  .
• If you fully charge the high-voltage battery, you should drive off shortly afterwards if possible – or plan charging with a departure time in the Infotainment system Timer-controlled charging.
• Avoid frequent charging with direct current (DC
  ) in everyday life.

 

L


Looks like some idiot has transposed the battery care section from the BEV handbook into the GTE handbook.

There was nothing like that in the handbook for my Mk 7.5 GTE. It served us well for three and a half years without detectable battery degradation. And it certainly had none of that impossible cosseting.

I sincerely hope that they haven't "increased" the battery size by reducing the protective top and bottom buffers, leaving you with a vulnerable battery in normal use.

 

I could set it to charge limit to 80% and battery hold to 20% (there are no 10% increment). That way I would have real world range of about 40 miles. Rather defeats the point of having a large 19.7 kWh battery. I think I will leave it on 80% and ignore the fact that it might sometimes end up with 0 miles of range. Before long journeys charge it to 100%.

 

Found the following on the Volkswagen Newsroom dated 5 March 2024 -

“19.7 kWh high-voltage battery. The new Passat eHybrid will enable electric WLTP ranges of about 100 km. Previously, it was up to 57 km. The significant increase in range is achieved thanks to a new high-voltage battery. Its net energy content increases from 10.6 to 19.7 kWh compared with previous versions (gross: 13 to 25.7 kWh). The battery has a new cell technology for the 96 modules and external liquid cooling. Since the lithium-ion battery is also positioned in front of the rear axle, the interaction with the front-mounted drive (electric motor, DSG, TSI) results in balanced weight distribution.”

So the battery is a surprisingly large 25.7 kWh. Playing with figures I suspect at 100% the battery capacity is the 25.7 kWh. At 80% 20.56 kWh. This might mean that at ‘0’ miles range the battery is damagingly depleted at a mere 0.86 kWh.

All I want to know is what is the buffer when the range has dropped to ‘0’ miles.
Anyone know?

 

When the battery on my Mk7 was at 0%, it was actually at 5% according to the internal BMS, but the cell voltages themselves were around 3.4V/cell. That is actually closer to 20% SoC if you were to try to extract all of the energy, without causing damage. The higher buffer here is used to provide hybrid functions, engine stop/start etc.

The issue with a PHEV battery is it is often required to start the engine. With that battery being nearly flat, if it is very cold outside (-10C to -20C) there is a risk that the engine may not start. This may be one reason on the Mk7 a larger buffer was reserved. That car in fact could not guarantee engine start below -30C ambient due to the small battery being so current limited.

Realistically, this is not an issue in the UK, but I suspect that's where the warning comes from.

 

With my previous GTE (Mk8) it was well known that the drive battery had a capacity of 13 kWh, 10.9 kWh available. No such information is available for the Mk8.5. Like you say there must be some reserve (buffer) when the mileage shows ‘0’ or the car wouldn’t start nor would there be any ‘boost‘ to do a full power overtake despite the ‘0’ miles showing on the dash (without the latter it could be embarrassing/dangerous).

 

I know the Mk7 GTE offered no boost, and reduced boost, when the EV battery was low. At 0 miles you got none, at 1-2 miles typically around 50% boost, and 3+ miles would usually offer full boost unless the battery was very cold. The car would try to get the battery state of charge to around 50% when driving in GTE mode, to give you maximum regen/boost capabilities.

 

I know with my Mk8 I had boost available when the range was showing ‘0’. Near the end of a long journey when the range was inevitably on ‘0’ a seriously quick overtake was always available. As soon as that manoeuvre was accomplished the engine would immediately start to charge the battery to top up the reserve. Not yet tried on my Mk8.5 doing a fast overtake with the range on ‘0’ since I have done very few journeys when the engine is required. I suspect it would be no different.

 

It's probably got a much larger buffer below zero then, also being a higher capacity battery it will be able to output more power even at a low state of charge.

 

Tom66 many thanks for your responses.

According to My Volkswagen App my all electric journeys indicate around 3.2 miles per kWh. If one multiplies 3.2 by 19.7 (net) it comes to 62 miles. Multiplying 3.2 by 25.7 (gross) it is 82. These are the two figures often banded about by Volkswagen.

Sadly this looks like there is probably Sweet F*** A** buffer or boost at zero range. VW appear to have made the this PHEV into a low range BEV with an engine. I hope I have got my figures wrong.

 

This morning I have received the following from VW Customer Services :-

“I understand how important it is to have clarity on your vehicle's battery performance, especially regarding the electric range.

I’ve consulted with our Internal Technical Team, and Owen from the Technical Department has provided some insights. While there isn't a definitive figure for the remaining kWh when the electric range shows ‘0’ miles, your vehicle is equipped with a 19.8 kWh high voltage battery. It's important to note that battery usage typically ranges between approximately 15% and 95%.

For a more detailed explanation and tailored advice, I recommend contacting your retailer directly. They will be able to provide you with the most accurate information specific to your vehicle.”

Concluded that when the battery range is on ‘0’ there is 15% charge remaining.

Do you think I am interpreting this correctly?

Regarding contacting my retailer - that would be a waste of time. They wouldn’t have a clue!

 

Did you get any further clarification with this as I was wondering the same.

I didn’t know the gross level was 25 until you pointed it out. Good spot.

I think what you say makes sense at 15% lower and 95% upper. And it makes sense regarding what it needs to keep this for. This would also work out number wise wouldn’t it ? I.e take 20% (5% upper and 15% lower) off of 25.7 and you do get almost 19.7. Give or take they have appeared to round things up or down.

As they also removed the battery charge mode whilst driving on the 8.5 I suspect that the lower buffer must be significantly large.

Otherwise like you say if on a long journey with lots of start and stop and use up electric at start then it wouldn’t be able to start again.

I have ran mine at zero percent and I think from memory it was still allowing me to run short distances on electric before ICE kicked in. Which if it was that low it would have left ICE on all the time I suspect.

 

You could get an answer with OBD-11, just access the BMS unit with the battery at 0 miles it'll tell you the real SoC as the car sees it, usually there will be a display SoC and raw SoC, the raw SoC is what you want.

On GTE Mk7 I recall it was around 4-5%, battery cell voltage of 3.4V.

Note that an NMC lithium ion cell can be discharged to around 2.7V before there is risk of damage. Between 2.7V - 3.4V is more like 10% capacity remaining. So the car probably cuts off around 3.1V/cell (5% actual 'safe' capacity remaining, giving a margin of 5% before battery damage happens.) If you get that low, it would require charging the battery externally, since the HV battery will not let you start the engine at that point.

I wonder how cars like Priuses cope when left for very long periods of time, they presumably cannot start the engine if the HV battery is completely dead, but have no way to recharge it. So they must have a much wider margin to allow for 6+ months without use, to avoid an expensive 'bricking' fault.