Battery Heating

[WalkingBootWeather]

TL;DR How should battery heating be used?

Strategies for pre-heating the traction battery were hinted at on last night's podcast but I feel more confused than before. I'm posting this on the MG4 thread but I daresay strategies apply equally well to the ZS mk2 and 5 too. I'll throw a few bulletted points out there to aid discussion but would be grateful for info and advice as to best practice.

• Sounds like battery heating is only worth doing when undertaking longer journeys in cold conditions. Not sure what constitutes a long journey or cold temperature - I'd guess 100 miles + and temperature less than 5 degrees C?
• It is necessary to turn battery heating on and off manually? Battery heating is not turned off when car is turned off and on again? Running the car with battery heating turned on when not necessary will be detrimental to range (more energy used heating the battery than efficiencies gained from operating with a warm battery)? Don't just leave it on!
• It was suggested that pre-heating is useful before departing on a long journey for about 1 hour? Presume this uses energy from charger and doesn't reduce battery SoC? This being the case then the car needs to be plugged in but does it matter if it is currently charging or not? If you don't have an hour before you need to depart is there still benefit in heating for 10-15 mins?
• It is worthwhile turning battery heating on when approaching a rapid charger if it is cold. Again how long before reaching the charger, and at what temperatures? Is even 5 mins heating helpful or is there a threshold temperature that needs to be reached before you get any benefit? Is the benefit only for higher rated chargers or is it still worth doing when approaching a 50kW rapid?
• If the plan A rapid is unavailable, do you simply continue to heat battery while seeking out plan B or can you overheat the battery?
• Has anyone done any real world testing and able to propose difference in charging speeds experienced between a cold and heated battery?
• Any other tips to efficiently travel longer distances in winter (increasing charge speeds and range)

Confused

 

[siteguru]

Re. battery heating whilst plugged in ... my experience is that (like with cabin pre-heating) the car must be actively charging for battery heating to work whilst plugged in. If the wall box is in standby mode waiting for a signal from the car then battery heating (at least via the app) won't start.

 

[Ian Key]

Doing some very rough calculations...

It was mentioned on last nights podcast that the heater for the battery uses 7kW/h
A video on YouTube shows the car being charged for 30 minutes before using a fast charger but that was for normal temperatures but during the recent cold snap it would probably take an hour.
Most drivers were getting 2m/kWh where as with a preheated battery it could be 3.5m/kWh. Or put another way unheated is 0.5 kW/mile increasing to 0.285 kW/mile when pre heated. An increase of 0.215 kW/mile.
To break even when preheating the battery for 1 hour it would take a journey of 32.6 miles.

No doubt someone will disagree with my calculations

 

[WalkingBootWeather]

Re. battery heating whilst plugged in ... my experience is that (like with cabin pre-heating) the car must be actively charging for battery heating to work whilst plugged in. If the wall box is in standby mode waiting for a signal from the car then battery heating (at least via the app) won't start.

Helpful, thanks. Do we think this is a design decision or a bug that may or may not be addressed?

It seems like a reasonable thing to want your car to be fully charged and with a battery warmed to an optimal temperature before setting off on a long winter journey. If you know the departure time it should be possible to schedule this in advance and not have to get up in the middle of the night shouldn't it?

 

[WalkingBootWeather]

Doing some very rough calculations...

It was mentioned on last nights podcast that the heater for the battery uses 7kW/h
A video on YouTube shows the car being charged for 30 minutes before using a fast charger but that was for normal temperatures but during the recent cold snap it would probably take an hour.
Most drivers were getting 2m/kWh where as with a preheated battery it could be 3.5m/kWh. Or put another way unheated is 0.5 kW/mile increasing to 0.285 kW/mile when pre heated. An increase of 0.215 kW/mile.
To break even when preheating the battery for 1 hour it would take a journey of 32.6 miles.

No doubt someone will disagree with my calculations

Thanks Ian, that gives us something to work with. I guess there will be lots of variables such as ambient temperature and how far & fast you are driving / braking as these will impact amount of additional energy needed to get the battery in to the 'Goldilocks zone'

One concern I have, based upon my experience of 3 years living with a ZS is that sometimes it seems that MG are driven by hard threshold values e.g. if the temperature of the battery when charging begins is less than 20 degrees the maximum charge rate is 80kW, if it is more than 20 degrees you might get 135kW. If the ambient temperature is near freezing you might use 6 or 7 kW to heat battery and still be below a threshold value and hence not get much benefit.

It might not be possible to give absolute definitive advice, but at least give us some clues MG.

 

[Ian Key]

Thanks Ian, that gives us something to work with. I guess there will be lots of variables such as ambient temperature and how far & fast you are driving / braking as these will impact amount of additional energy needed to get the battery in to the 'Goldilocks zone'

One concern I have, based upon my experience of 3 years living with a ZS is that sometimes it seems that MG are driven by hard threshold values e.g. if the temperature of the battery when charging begins is less than 20 degrees the maximum charge rate is 80kW, if it is more than 20 degrees you might get 135kW. If the ambient temperature is near freezing you might use 6 or 7 kW to heat battery and still be below a threshold value and hence not get much benefit.

It might not be possible to give absolute definitive advice, but at least give us some clues MG.

Yes you're right. There are too many variables to give a definitive answer the biggest of which is the driver.
Probably the way to think about it is if the journey is over 40 miles non-stop and it's below freezing then it's worth preheating the battery.

 

[siteguru]

Helpful, thanks. Do we think this is a design decision or a bug that may or may not be addressed?

In terms of cabin pre-heating, MG are aware and plan to resolve this (time scale unknown). Whether this will also include the battery heating I don't know.

 

[Cocijo]

Fast (AC charging) does not stress the battery anywhere near what rapid charging does.

I think pre-heating (or pre-conditioning as sometimes it might need cooling) the pack for fast charging is seldom required unless it’s well below zero or very hot/been heavily used.

The key problem area (and I believe the main reason that battery pre-conditions exists) is if you’re rapid charging without pre-conditioning. What usually happens if the pack is not pre-conditioned, is the rate is reduced by the BMS to protect the pack, until the battery pack can take the increased rate (E.g. it’s warm enough).
This leads to longer charging times, and is why some car mapping software is set up to automatically start pre-conditioning when within a certain distance, if a rapid charger destination is selected.
Of course the issue here can be when you arrive at a rapid having used more range getting there pre-conditioning your battery to find that it’s not working…
Heating a pack prior to driving seems to be logical as we all know that battery packs perform better when the weather is warmer (they typically like about 20c best). Although having a manual option might be useful, I’m surprised that this function is not fully automated and set up based on key tested parameters. Otherwise it could have a negative effect and use more power rather than save any.
There’s clearly confusion on how and when to use the battery heating and this should not be the case. If fitted, it should be configured to both protect the battery and give the best blended approach to economy.

 

[MoDolph]

It's not going to be possible to answer a lot of these questions until us geeks have access to battery temperature data from the obd port. Hopefully it won't be much longer.

Until then, I plan to activate heating straight away whenever I know I'm going to be rapid charging. Once it's up to temperature it won't use much energy maintaining it.

Cycling the battery at higher temperatures also reduces degradation, so if your doing a long trip it might be worth activating pre-heating even if not planning on rapid charging but this is a complicated question of costs Vs benefit.

 

[WalkingBootWeather]

It's not going to be possible to answer a lot of these questions until us geeks have access to battery temperature data from the obd port. Hopefully it won't be much longer.

Surely MG must have some idea? I just wish they would give us a steer. But yes, I think you are right we will likely get some good info from enthusiasts over time.

Until then, I plan to activate heating straight away whenever I know I'm going to be rapid charging.

But when? Whenever you are on a journey that needs a rapid charge, or only when it is cold, and if so how cold? Will you pre-heat before you depart or just on route? If on route at which point on the journey?

Unless we know how and when to heat the battery we will likely end up doing it wrong and either not use heating when we should, or waste more energy heating than we save.

Maybe we just forget the function exits, after all many of us managed without it in our previous EVs?

 

[WalkingBootWeather]

Update. This video suggests turning on intelligent battery heating about 30 mins before rapid charging in very cold conditions and achieves impressive charging speeds when done.

 

[MoDolph]

But when? Whenever you are on a journey that needs a rapid charge, or only when it is cold, and if so how cold? Will you pre-heat before you depart or just on route? If on route at which point on the journey?

It shouldn't really matter. I'm guessing that the battery heater will heat the battery to the optimum temperature, likely 25C, and then maintain it so it should be fairly foolproof.

I'd turn it on every journey where I know I'm going to be rapid charging and range isn't an issue.

Also, I'm extra cautious about degradation since we plan to keep it for 10 years so would try to pre-heat before subjecting the battery to a big discharge cycle if it was <5C.

 

[Dan C]

I personally have kept the “intelligent”battery heater switched off ( I’ve not intelligent in the slightest, as soon as you enter the car when it’s cold it heats the battery, rather than pre-heating the battery before a rapid charge like a Tesla etc )

I found my range was shocking with the battery heater on as I do lots of short journeys, now I have the heater off I can get 120 miles ish out of a charge doing lots of short journeys ( heating the cabin every time does decrease your Miles per KW somewhat )

 

[Tig170]

Doing some very rough calculations...

It was mentioned on last nights podcast that the heater for the battery uses 7kW/h
A video on YouTube shows the car being charged for 30 minutes before using a fast charger but that was for normal temperatures but during the recent cold snap it would probably take an hour.
Most drivers were getting 2m/kWh where as with a preheated battery it could be 3.5m/kWh. Or put another way unheated is 0.5 kW/mile increasing to 0.285 kW/mile when pre heated. An increase of 0.215 kW/mile.
To break even when preheating the battery for 1 hour it would take a journey of 32.6 miles.

No doubt someone will disagree with my calculations

Thanks for the clear explanation! - appreciated - it looks like if your are on a fixed 24 x 7 tariff it might BE worthwhile, but if you are on time of day (such as myself, where cheap rate ends at 5am), and I dont need the car until 8am, then it might NOT be worthwhile given that cheap to peak rate is 10:1 (4.5p night to 45p day)??

 

[WalkingBootWeather]

I personally have kept the “intelligent”battery heater switched off

For efficiency I suspect this is the best strategy when undertaking short journeys however it might be kinder to your batteries health to pre-heat when especially cold (below freezing) and my gut tells me it might be worthwhile for longer trips (40 miles/1 hour or more at 5 degrees or less) but it is guesswork

I'd turn it on every journey where I know I'm going to be rapid charging and range isn't an issue.

Every journey? Even in summer? If the heater really is intelligent I guess it wouldn't turn on if the ambient temperature was warm so maybe you are right.

 

[amdmad]

I presumed battery heating was for turning up at a rapid? If you can remember to turn it on ?