Best practice for charging LFP batteries on MG4 se

I believe the BMS calibration (<10% - 100%) is best done in one uninterrupted charge. But you don't need to do this often.

The LFP battery prefers to be charged to a 100% and if I'm not mistaken your car won't have an option to set a charge to less than that anyway. (I have a trophy though, so can't comment from experience).

Once a month or so you should balance charge the battery, which again, as far as I know happens at 100% charge.

Ok thank you. I thought that with octopus go you set the desired charge percentage through the octopus app. So I guess I should always set it to 100%.

Just about all the information on the interweb is based on anything from what they said at the pub to what they understood from reading papers written by enterprises that were using rapid aging techniques in an attempt to get the results in a few weeks rather than over 10 yrs.

My experience is with LFP house systems, 12v, 24v and 48v systems. I set them up to charge to 100% every day if there is enough solar, but the bit no one mentions is what cell voltage they are using to determine 100% SOC.
From 12 yrs and around 250 systems experience, fully charged is a resting voltage of 3.5v, 98% charged is a resting voltage of 3.4v. Neither can be achieved charging at 3.4v per cell.
I'm still waiting for a scanner to see what the end voltage is on my 51 to see what the MG BMS considers fully charged .... and hopefully a way to see every cell voltage ....

T1 Terry

You clearly know your stuff Terry. So would you concur that it is best practice to charge to (what the car tells me) is 100% every day, and should I occasionally charge to 100% uninterrupted (and if she, how often?). Cheers

Assuming it's a Zappi being fitted - you request on the Octopus app a % to add and the time you need it completed by.

If you keep adding repeated small percentages then it will always do it inside the core hours of 23.30 - 05.30. However if you let it run down to 10% then ask for a charge to add 100% by 4am and start the charge at 20.00 it will charge from plugging in until 4am. The whole house will also then benefit from cheap electricity during this period so this will work out cheaper than lots of small charges.

Tight Git said:

Assuming it's a Zappi being fitted - you request on the Octopus app a % to add and the time you need it completed by.

If you keep adding repeated small percentages then it will always do it inside the core hours of 23.30 - 05.30. However if you let it run down to 10% then ask for a charge to add 100% by 4am and start the charge at 20.00 it will charge from plugging in until 4am. The whole house will also then benefit from cheap electricity during this period so this will work out cheaper than lots of small charges.

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Thank you

Jonperry64 said:

Thank you

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Just to clarify, in your second scenario, the whole house gets cheap rate electricity from 8pm to 4am? If so that's very handy!

As long as Octopus are controlling the charge and the slots are allocated and the car is charging - they are at 7p/kWh and the whole house is at the cheap rate

Attached is a day showing the cheap rate charged from 8pm

I've just done my first sub-10% to full charge in one session on a Tesla Wall Connector (took a bit over 7 hours). The car thinks it's got 409km in range. I'm assuming that's best case scenario, as in ECO mode and no A/C? Either that or the calibration didn't work properly?

My previous 500km or so averaged around 14kWh, which is around 365km range.

Just use it like your phone, so if its low, then charge it fully up until the next time the car is getting low. Avoid plugging it in every night to keep it at 100%. We have a LFP home battery system with batterview (below), so my experience is with that more that the MG4 SE. The cells appear to be balancing 24x7, once in a while (monthly) charge to 100% as it recalibrates all the cells to their max capacity.

99% of the time Intelligent go will start to charge as soon as you plug in. but it can a pain with home batteries, as unless you tell your invertor (or MG4) it will drain the home battery before the car. Of course its ideal if you are a very heavy user (we use 1.5MWh / month in winter), as you can plug in the car when the home battery is getting low, which charges both at the same time. We have set a non MG4 profile in the charger which limits charge rate to 3.44kW, as it spooks me when I see 10000W+ on the live data from the octopus app.

Wizard of Oz said:

I've just done my first sub-10% to full charge in one session on a Tesla Wall Connector (took a bit over 7 hours). The car thinks it's got 409km in range. I'm assuming that's best case scenario, as in ECO mode and no A/C? Either that or the calibration didn't work properly?

My previous 500km or so averaged around 14kWh, which is around 365km range.

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The range should change/update when you select eco mode and turn the A/C on or off. I think the car gets a little confident when you’ve done a calibration. The range will probably return to your expected range soon

ReintjeWA said:

The range should change/update when you select eco mode and turn the A/C on or off. I think the car gets a little confident when you’ve done a calibration. The range will probably return to your expected range soon

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Yep, as soon as I got into the car this morning, with A/C and Normal Mode on by default, the range instantly dropped to 388km.

Hmmm...... looks like we might have to change our driving style, I thought I was doing ok at 17kWh/100km, down from the 22kWh/100 when we first picked it up, that EV grin as you move off from a stand still or pull out to over take is still new and might take a while the settle down a bit .... or it may never settle down.
The Gen 2 Prius only gets close to the 4.5ltr/100 on a long trip, otherwise it's up around the 5.5 to 6.5 maybe I should drive with lighter shoes

T1 Terry

the first km is around 17 kWh/100km, but after 10km @ 70 km/h it drops down to 11 or 12.
On the highway @ 110 it's 15 or 16.

I’ve been averaging 18 kWh/100km but I currently do mostly short city drives. It drops to the 15/16 range on the highway like @decrep said. I honestly don’t really care, it’s cheap to charge anyway so I just have fun with it.

Jonperry64 said:

You clearly know your stuff Terry. So would you concur that it is best practice to charge to (what the car tells me) is 100% every day, and should I occasionally charge to 100% uninterrupted (and if she, how often?). Cheers

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Basic rules for all lithium technologies are:
Only charge to 100% if you’re using it the next day (but an occasional full charge to 100% is good for battery health
Don’t charge to 100& on DC fast chargers unless you really need to … DC fast charging is stressful and promotes dendrite growth which is what kills 99% of batteries eventually, AC slow charging isn’t stressful.
If you’re not using the car for a while, don’t leave it at much above 80%; some manufacturers suggest lower values but as a rule of thumb that’s a good, safe value.
Don’t leave your car stored at too low a charge for more than a few days, depending on the make and model but for the MG4 less than 50% is likely to prevent the car topping up the 12V battery (exact % I’ve never found, it’s vague in the manual but 8 do know that less than 30% and it definitely doesn’t top up the battery!)

Don’t leave the car plugged I
In but not charging while you’re away on holidays etc. no problem for the main battery, but in the MG4 the car won’t top up the 12V battery if plugged in and not charging! (Several experiments on that one between myself and another owner!)

Yes, I do know about batteries of all types (work related) and a house LFP works a bit differently to an EV, there’s a reason they typically have shorter warranties! They also tend to have different regular charge cycles to an EV, as they are designed to use the surplus to charge from solar (although you can grid-shift by charging from the mains, which I do but the benefit is good!).

Above all don’t get too hung up on the best way to charge your battery, the BMS takes care of the hard part but don’t make it a stress point like range anxiety, just enjoy the drive and the fuel savings!

Not just an ordinary Youtuber........

There's no reason to charge the LFP everyday to 100%. While it's true, that chemistry doesn't degrade heavily, if regularly charged to 100%, it still isn't the best way to keep the battery in good health for a long time. LFP will still benefit from extra cycle life and slower calander aging if kept below 100% all the time.

The reason why MG (and many others) don't even give you the option to limit charging is due to the way BMS usually balances and calibrates itself. LFPs generally like to be top balanced. And to always have accurate SOC, you need to regularly cycle to 100%, otherwise BMS can drift away and get inaccurate. I've seen (not on cars though) BMS drift away for as many as 30-40% when not regularly charged.

PerthPete said:

Not just an ordinary Youtuber........

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I almost left it after a couple of minutes but glad I stayed with it. Very well researched and presented, I like this guy!