Should LFP batteries be charged to 100%?

[Ozboz7]

I work in the battery world but other opinions will exist!

80% is often cited as an optimal charge level. the less energy you store in the battery the more relaxed it is and the less damage caused. Think of the cell like a balloon filled with water, you can fill it to absolutely full but it'll be very stretched and tight and will become weaker

Another aspect of 80% is this is about the point that the pack reaches full charge voltage and switches from a constant current to constant voltage phase.

Charging to 100% for LFP makes some sense, as said they have impressive cycle life even with full charge and discharge, so it will degrade the cell but by an appreciably smaller margin than for the Li-ion pack. LFP will often achieve 2000 - 5000 cycles. Hence why Tesla isn't bothered about you charging to 100% to maximise range as you'll still get more cycle life.

My own way of using my car is to charge to about 85% once a week timed to finish by the time I'm about to do a commute.

Was in this very bloody thread gonna ban myself from making posts post-nights

 

[ACarneiro]

Was in this very bloody thread gonna ban myself from making posts post-nights

Oh, au contraire!
I find these posts to be informative and stimulating and I learn so much from them!

 

[kelvin 660]

The way I read it is charge to 100% daily or at least once a week to 100% and in addition let it sleep (after charging) by disabling sentry at the location where you charge.

LFP chemistry is very stable when charge to 100% and will not normally age the battery.
See

for why this is and other advantages of LFP batteries...

 

[Lord Farquad]

I have to admit, I’ve got a MYLR on order and will really miss the LFP. If they used LFP in MY I’d be very happy.

 

[MrT3]

The way I read it is charge to 100% daily or at least once a week to 100% and in addition let it sleep (after charging) by disabling sentry at the location where you charge.

LFP chemistry is very stable when charge to 100% and will not normally age the battery.
See

for why this is and other advantages of LFP batteries...

LFP will have accelerated ageing if left at a high SoC. But the amount is much less than other battery types, and certainly not enough for Tesla to worry about it affecting their warranty so convenient trumps ultimate battery care in their advice.

 

[Leeroy]

I have an early LFP model 3, April 2021 build with 50,000km. I charge as per instructions once a week to 100%. The car showed 422km when new and snuck up to 424 a few months after. Now showing 412 when full. LFP will still degrade as has been mentioned, but at a reduced rate (hopefully!!)

 

[positiv]

LFP chemistry is very stable when charge to 100% and will not normally age the battery.

That statement gives me alarm bells. LFP certainly has a shorter cycle life at 100%. Going to 80% DOD instead will more than double your cycle life.
Whether this makes a difference over the life of the vehicle I'm not sure. Tesla might also be using a top buffer so that 100% isn't really 100%.

 

[Jason71]

That statement gives me alarm bells. LFP certainly has a shorter cycle life at 100%. Going to 80% DOD instead will more than double your cycle life.
Whether this makes a difference over the life of the vehicle I'm not sure. Tesla might also be using a top buffer so that 100% isn't really 100%.

they will be. it isn't but it will still be near enough to cause more degradation than say 80%.
The charge to 100% is about BMS ( as mentioned in here a long time ago) LFP voltage varies very little with state of charge so BMS needs the charge to 100% to stay calibrated. does not mean its not a bit bad for the actual battery and you dont have to leave it there for long.
Best way is to charge to 100% then set off soon after. Obviously not very compatible with Octopus Go or other off peak charging solutions.
Unless you plan to keep the car a very long time though probably not your problem anyway

 

[SR-Plus]

My LFP Nov21 model has done 6k miles.
I charge to 100% at least once a week, sometimes it sits at 100% for a couple of days at a time. When I first bought the car, the range was showing me 273/272 and now it’s 265. It’s had 3 supercharger sessions in that time. I think as with most Tesla’s, at least what I’m hoping for my car, is that most of the degradation happens in the first year or two and then tails off.

 

[kelvin 660]

Looking at the available data, it looks like LFP is good for at least 3,000 cycles, if not more...

ShieldSquare Captcha

iopscience.iop.org

Given each cycle is good for ~200 miles that equates to 600,000 miles. I don't think we need worry about charging to 100% and I will follow Tesla's recommendation.

 

[qwickshot]

I’d still only charge the car to 100% if you know you are going to use it the next day, LFP or not.

It’s not that critical to charge it to 100% all the time, just doing it regularly is more than enough enough. When I say regularly it’s based on how you use the car and cycle the battery, for example more use means more more 100% charges.

It’s worth noting that degradation impacts more than range, it impacts power output and rapid charging.

 

[Ozboz7]

Only had my car for 1.5k miles, but have had no issues with my charging limit set to 85% - if I know I need the extra range can just change the limit to 100% in the app - or stop at a supercharger. Each to their own decisions though!

 

[Buzzliteyear]

I don't have a regular charging schedule, most of the time I part charge while shopping or use the mobile connector. If I am going away at the weekend then I will go to 100%

 

[kelvin 660]

Only had my car for 1.5k miles, but have had no issues with my charging limit set to 85% - if I know I need the extra range can just change the limit to 100% in the app - or stop at a supercharger. Each to their own decisions though!

The problem is that the BMS becomes less accurate over time/charges when you don't charge to 100%, due to the flat nature of the charging curve. That may result in the BMS may report a SoC of 85% when in reality the battery only has 75% SoC. That's not a big problem until you go to a low state of charge and find you've run out of battery, when it said you had 5% left!

You may think that charging to 100% every few months will reset the BMS, but if that was the case then I'm sure Tesla would have said so...

 

[kelvin 660]

Some more info on charging LFP batteries to 100% from a battery expert...

 

[MartiMart]

Always charged my M3P to 90% each night when leccy is cheaper, which is recommended by Tesla. Also keep plugged in whenever at home.

 

[Adopado]

Always charged my M3P to 90% each night when leccy is cheaper, which is recommended by Tesla. Also keep plugged in whenever at home.

That's fine but let's not forget that this thread is specifically about LFP batteries, which an M3P doesn't have.

 

[Ozboz7]

The voltage still does jump up at around 100% though (have a look at lifepo4 discharge voltage curves). I hope that Tesla have a buffer that negates some of this - that would be the sensible idea. (PS I'm not trying to scare anyone etc with this chart - LFP chemistry has less degradation compared to other chemistry at high-er SOC)

For my use case anyway I want to keep this car and its battery health for a long time, so personally will avoid higher SOC where practical.

The voltage does again drop below 20%, so (again, for my personal use case) I'm relatively happy accepting the theoretical risk of BMS miscalculation by not regularly charging to 100%

Edit: this is based on 12v not single cell hence different V values

 

[kelvin 660]

But even at the worst case of 100% SoC = 3,200 cycles then at 200 miles per charge (3,200 x 200) = 640,000 miles!
Most ICE cars don't get to 250,000 miles (OK a few do...)

Also there must be a top buffer otherwise regen would have no affect at 100% SoC, whereas it does have some regen.

 

[doats1]

Practically you’re not getting 200 miles per charge unless you’re always on the motorway. So that number looks inflated even with LFP batteries.