High Voltage (HV) Battery - Best Charging Practice?

[TetchyTechie]

There's an informative thread over in the MG4 section about Balance Charging:

Balance Charging - a few questions

A few EV noob questions I have had my phase 2 Trophy for about 2.5 months now, and as it is owned not leased, I am keen to keep the battery in as good a state of health as I can. With that in mind I have been cycling it between around 20-80% as per recommended practice. The thing is that we...

www.mgevs.com

My question, born of ignorance, is whether there are any 'Best Practice' documented procedures for keeping the HV battery in good shape?

In my previous EV, I only ever charged to 100% by accident - I charged to a State of Charge (SoC) of 60% for daily driving, with the battery going down to about 40%. If it went slightly lower, I had it set to charge immediately to 40%, then top-up to 60% overnight. Charging was done at 5 amps (the minimum possible),

On long trips, I would charge up to just over 80% at the fast chargers - the 'knee' of the charging curve for that EV - shown when the power output of the charger dropped quickly from the maximum.

When I traded it in, the battery was still showing full range (in a 9-year old car), so it had not used up all the built in (hidden) flex-capacity - in other words, it still had at least 80% real capacity.

I'd like to do the same with the MG5, which doesn't have an easy built-in capability to charge at a maximum of 5 amps - you can set the 'granny-charger' to do this, but not the car's main system, and my wall charger is not sophisticated enough to do it either.

The Energy Management display of the MG5 highlights a range between 40% and 80% to keep the battery in good condition. Does this mean that optimally, the battery should not drop below a 40% SoC, or be above 80% (for long)?

What is the best SoC to keep the battery at? My understanding for Lithium-ion cells (which could be laughably wrong) is that charging them to cycle a close as possible to the 50% level allows for the most recharge cycles - so charging to 60% overnight, doing a daily drive down to 40% and recharging to 60% overnight is about the best you can do - but I'm happy to be guided by an expert (with references/Internet links where possible).

Some publications claim a difference between Lithium Iron Phosphate cells and Lithium Nickel Manganese Cobalt (NMC) cells, in that the former tolerate being charged to 100% far better than Lithium NMC cells, but Lithium NMC cells have better cold-weather performance. I don't know which chemistry the MG5 batteries are, and would like to find out - anyone know how?

At the moment I'm getting a long-term efficiency of 14.3 kWh per 100 km (which is 7km per kWh, or roughly 4.4 miles per kWh) (The old EV allowed me to switch between kWh per 100 km or km per kWh, which I prefer. It doesn't seem to be possible to switch similarly in the MG5, but my mental arithmetic is getting better.) This means that at 50% charge, on the 'Eco' setting, it claims a range of 230 km. Given the rated range of a 100% battery is 380 km, that looks like a good result. I doubt it will last into winter, though.

So, what's the best (practical) regime for caring for the battery?

 

[MickeySw]

In my previous EV, I only ever charged to 100% by accident - I charged to a State of Charge (SoC) of 60% for daily driving, with the battery going down to about 40%. If it went slightly lower, I had it set to charge immediately to 40%, then top-up to 60% overnight. Charging was done at 5 amps (the minimum possible),

6A min for MGs

On long trips, I would charge up to just over 80% at the fast chargers - the 'knee' of the charging curve for that EV - shown when the power output of the charger dropped quickly from the maximum.

Same applies to MG5

When I traded it in, the battery was still showing full range (in a 9-year old car), so it had not used up all the built in (hidden) flex-capacity - in other words, it still had at least 80% real capacity.

7year battery warranty guarantees 70% SoH

I'd like to do the same with the MG5, which doesn't have an easy built-in capability to charge at a maximum of 5 amps - you can set the 'granny-charger' to do this, but not the car's main system, and my wall charger is not sophisticated enough to do it either.

No built in current selector, but you can easily get a type 2 ‘granny’ with variable charge currents

The Energy Management display of the MG5 highlights a range between 40% and 80% to keep the battery in good condition. Does this mean that optimally, the battery should not drop below a 40% SoC, or be above 80% (for long)?

What is the best SoC to keep the battery at? My understanding for Lithium-ion cells (which could be laughably wrong) is that charging them to cycle a close as possible to the 50% level allows for the most recharge cycles - so charging to 60% overnight, doing a daily drive down to 40% and recharging to 60% overnight is about the best you can do - but I'm happy to be guided by an expert (with references/Internet links where possible).

There are as many opinions as there are ‘experts’ on this topic, keep your ‘old regime’ as it seems to have worked well for you.

Some publications claim a difference between Lithium Iron Phosphate cells and Lithium Nickel Manganese Cobalt (NMC) cells, in that the former tolerate being charged to 100% far better than Lithium NMC cells, but Lithium NMC cells have better cold-weather performance. I don't know which chemistry the MG5 batteries are, and would like to find out - anyone know how?

All long range MG5s have NMC batteries, there is also a label on the battery pack.

At the moment I'm getting a long-term efficiency of 14.3 kWh per 100 km (which is 7km per kWh, or roughly 4.4 miles per kWh)

That’s about as good as it gets driving on 17” rims

The old EV allowed me to switch between kWh per 100 km or km per kWh, which I prefer. It doesn't seem to be possible to switch similarly in the MG5

You can only set the units from metric to imperial, no other options

This means that at 50% charge, on the 'Eco' setting, it claims a range of 230 km. Given the rated range of a 100% battery is 380 km, that looks like a good result. I doubt it will last into winter, though.

No, it won’t, how much you ‘lose’ largely depends on ambient temperature

So, what's the best (practical) regime for caring for the battery?

Don’t use it..

Joking aside, keep the SoC between 30-80%, balance regularly (about once a month), do a calibration charge twice/year, avoid DC charging and use low AC current seems to benefit battery health in the long run.

 

[Gomev]

..

No, it won’t, how much you ‘loose’ largely depends on ambient temperature

..

Lose.
Just saying Sorry but it's just one of those things that I hate seeing.

 

[MickeySw]

Lose.
Just saying Sorry but it's just one of those things that I hate seeing.

Sorry, the hour was late, corrected…

 

[Alibro]

I might live to regret this but to my mind life is too short to worry about a few percent drop in battery capacity. When my tariff switches to economy 7 (or EV tariff) I'll plug the car in when I get home and let it charge to 100% every time I charge it. This will not be every night but maybe a few times per week.
What I will not do is leave it at 100% for long periods which should hopefully mitigate a little.

My mobile phone is now 4 years old and has been charged to 100% every other day since I got it and I don't see any degradation worth talking about. I believe this is because modern batteries are more resilient than the type installed in early Nissan Leaf's.

 

[pollenface]

I have a 15A rate-selectable "granny" from Ebay, it works on 80-250VAC 50/60Hz.

I'm thinking of getting a 120V inverter for my off-grid so I can charge at half rates, less load on the off-grid system during overcast days.

1500W @ 240V = 750W @ 120V

 

[CanyonReveller]

I have a 15a rate-selectable "granny" from ebay, it works on 80-250vac 50/60hz

I'm thinking of getting a 120v inverter for my off-grid so I can charge at half rates, less load on the off-grid system during overcast days.

1500w @ 240v = 750w @ 120v

Do you use it at 15a often? I have a similar one rated to 16a, but I'm reluctant to use it at the full capacity as it seems a bit much juice for a standard 3 pin plug.

 

[pollenface]

Do you use it at 15a often? I have a similar one rated to 16a, but I'm reluctant to use it at the full capacity as it seems a bit much juice for a standard 3 pin plug.

Yes, nearly all the time if charging from grid power ... I put in my own circuit for it with 10mm2 cable and 25a breaker, really it never actually operates at more than 14.3a.

 

[Alibro]

Do you use it at 15a often? I have a similar one rated to 16a, but I'm reluctant to use it at the full capacity as it seems a bit much juice for a standard 3 pin plug.

I had a 3kW (15A) charger plugged into a 3pin plug for a few weeks but it damaged the socket.
It is very much not recommended.

 

[5teep]

We're talking about 20plus year useful lifespan for HV batteries, just AC charge as often as you can and don't worry about it.

 

[Verdigris]

An interesting video particularly pertinent to people who mainly use the car for fairly short journeys:

 

[TetchyTechie]

An interesting video particularly pertinent to people who mainly use the car for fairly short journeys:

I'll have to look at the longer video and read (at least) the referenced paper.
My usage is daily pootling around town with approximately bi-monthly long trips that in the old EV took multiple 'fast' recharges with a lot of range anxiety. It's no fun coming to the rest-stop on a motorway to find the single charger is out-of-action, and you need to drive very conservatively to get to the next one. I've also had the fun and games of occupied chargers with the car owners nowhere to be seen, and a deadline to get to the ferry. All fun.
It's one of the three main reasons I chose the MG5 - the additional range makes life so much easier.

Battery chemistry will influence the best charging regime - Lithium Iron Phosphate compared to Lithium Nickel-Manganese-Cobalt (NMC), and I'm still interested to know if it's better to keep the battery on a (say) 60% to 20% diet, or 70% to 30%, or 80% to 40% or something else, and the optimal level of charge when not using the car for 'a while'.

Thank you for the pointer to that video.

I had a 3kW (15A) charger plugged into a 3pin plug for a few weeks but it damaged the socket.
It is very much not recommended.

If your 3kW charger is drawing 15A, that implies a voltage of 200 Volts. If that's UK mains, it is out of tolerance, or your charger is dissipating a significant amount of heat - UK mains is 230 Volts (Actually 230 V nominal with a tolerance of +10% / -6% - it used to be 240V nominal with a tolerance of +6% / -6% - the historical and current tolerance ranges overlap) - 6% below 230V s 216.2V.
The testing of sockets allows for a certain temperature rise over a set period of time, with rest periods.. Drawing 13A (or greater) for longer will likely exceed the allowable temperature and damage the socket. You can get sockets specifically tested and marked for charging EVs - here is a link to one such as an illustration, not a recommendation: Tough Leads: 13A EV Sockets Compliant with BS 1363-2 EV
If I charge with a 'granny-charger', I personally keep the current at the lowest possible (usually 5A or 6A) to minimise the risk of over temperature at the socket or any other connection in the wires back to the 'fusebox'. Old installations can develop high resistance at joints and screw-fittings, and if it hasn't been spotted by a regular test, high current for long periods can be a significant fire risk.

 

[MickeySw]

and I'm still interested to know if it's better to keep the battery on a (say) 60% to 20% diet, or 70% to 30%, or 80% to 40% or something else, and the optimal level of charge when not using the car for 'a while'.

Let us know if you ever find a scientific answer but with battery technology these days it doesn’t make much (any?) difference..

 

[Deleted member 13103]

I might live to regret this but to my mind life is too short to worry about a few percent drop in battery capacity. When my tariff switches to economy 7 (or EV tariff) I'll plug the car in when I get home and let it charge to 100% every time I charge it. This will not be every night but maybe a few times per week.
What I will not do is leave it at 100% for long periods which should hopefully mitigate a little.

My mobile phone is now 4 years old and has been charged to 100% every other day since I got it and I don't see any degradation worth talking about. I believe this is because modern batteries are more resilient than the type installed in early Nissan Leaf's.

I charge mine exactly the same way, my EV tariff starts at 00:00 until 07:00 with no variation in the charging, sometimes as low as a 7% start, but by 07:00 it's only in the mid 90s%, I switch off at or before 07:00, my charger is a generic 7kW AliExpress special, defintately no frills, so cannot control anything other than a full on charge rate, though I do think it stops charging when the car is full 100% (hopefully).

 

[pollenface]

The charger is built in to the car, the lead is just a power supply.

 

[TetchyTechie]

Let us know if you ever find a scientific answer but with battery technology these days it doesn’t make much (any?) difference..

I will.

The manual is reasonably clear about long-term non-use of the car - the HV battery should not be allowed to drop below 50% SoC:

Preface​

• Do not park or store the vehicle for long periods with
  a low state of charge, where possible charge the vehicle
  as soon as possible prior to storage.

Starting & Driving​

• An equalisation charge must be carried out prior to
  using the car after a long period of storage or non use.
  In these cases the charging time will be extended.

Maintenance​

High Voltage Battery Pack​

• If the vehicle is not going to be used, parked,
  or stored for a long time it is necessary to
  charge the vehicle at least once every 3
  months. During this time, the High Voltage
  battery state of charge should not be allowed
  to drop below 50%.
• If the battery is in a low state of charge and
  the instrument pack displays no valid driving
  range, the vehicle MUST NOT be left in a
  stored state for more than 7 days without
  being charged to above 50%.
• Failure to follow these guidelines will result
  in HV battery damage and invalidate the
  warranty.

 

[Alibro]

I probably should have said more than a day or two rather than long periods which can mean anything.

I charge mine exactly the same way, my EV tariff starts at 00:00 until 07:00 with no variation in the charging, sometimes as low as a 7% start, but by 07:00 it's only in the mid 90s%, I switch off at or before 07:00, my charger is a generic 7kW AliExpress special, defintately no frills, so cannot control anything other than a full on charge rate, though I do think it stops charging when the car is full 100% (hopefully).

My EV tariff kicks in at midnight or 1am depending on the season so I'll set the timer on my EVSE (pretty much the only intelligent setting on a Vorsprung Nano) to start then which should give 100% charge most days.
I'm self employed and some weeks work every day but other weeks one or even no days so the car will only get a full charge when it needs it.

 

[shpub]

So, what's the best (practical) regime for caring for the battery?

• Plug it in when you need more miles.
• Drive it when you have miles.
• Life is really too short to do anything else.
  
  You will need a 100% AC charge to balance the batteries which is a good thing which really blows this idea of never going to 100% out of the water.
  
  DC charging to 80% is a good thing but the car will not suddenly start to vapourise at 80.1% charge. The main issue is that it hogs the DC charger because that last 20% can take forever due to the charge rate drop. While the car takes over an hour to gain that little bit extra, other irate owners are blocked from getting a charge. That is actually the main reason for not doing a 100% DC charge these days as the car systems will drop the charge rate accordingly and in doing so can control the battery temperature and other parameters.
  
  The car has some pretty sophisticated control systems to ensure battery health. They are constantly monitoring module voltage, temperatures of the battery and charger and a host of other data. It can do a far better job than most people think.

One final thing: the technical term for the dash display estimated mileage and battery percentage left is "Guessometer" because it is not accurate, repeatable and nothing more than a guess at what the mileage and battery SOC actually is. It is affected by so many variables that it is nothing more than an informed guess. It should not be taken as anything else.

 

[MickeySw]

One final thing: the technical term for the dash display estimated mileage and battery percentage left is "Guessometer" because it is not accurate, repeatable and nothing more than a guess at what the mileage and battery SOC actually is. It is affected by so many variables that it is nothing more than an informed guess. It should not be taken as anything else.

The car knows the actual SoC and past usage, however it can’t predict the future consumption..

 

[shpub]

The car knows the actual SoC and past usage, however it can’t predict the future consumption..

The car thinks it knows the SoC but it is a guess that could be 10% out. SoC is really difficult to measure, especially in an environment where the battery is constantly being discharged and charged at differing rates.