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Charging strategy

Drmouse

Member
Jul 25, 2019
71
29
UK
TL;DR: What charging strategy is everyone else using right now?

It's coming up on a year since I took delivery of my Model 3. Things are a bit different, now...

When I first received it, I was commuting around 40 miles per day. My charging strategy was very simple. I would set the charge limit to 80% and schedule for 00:30 (Octopus Go), plug in when I got home and unplug when I set off for work.

Now, both my wife and I are working from home, so we do very few miles. I had read that just leaving it to charge a tiny amount every night was really bad for the batteries, so I changed things up. I would charge to 80%, then reduce the charge limit to 60%. I wrote a small script to check if the SoC was below 65%, and increase the limit back to 80% again. This way, I was charging around once per week, and it always had plenty for the trips I needed to make.

Then, I had an "abnormal" day, and realised this was only optimal if I had time to plan. On this day, my wife had a dental appointment 30ish miles away. This was all well and good, even though I was starting at around 65%. We arrived home at about 40%, and I plugged the car up so it could charge overnight.

Unfortunately, we then got a call that my wife's sister was in hospital. It was nothing too serious and we weren't allowed in to the hospital anyway, but my wife obviously wanted to be on hand and wanted to bring her supplies in case she was admitted overnight. This left us with a problem: We knew we would probably be parked up for a couple of hours, at least, waiting for her to be seen (turned out to be over 6 hours). While I would not have been too worried about just a 60 mile round trip, adding the time spent sat in the car waiting with heating on etc, I was a little nervous.

Fortunately, we found a Tesco with a slow charger right around the corner, so we could park there and await the news while getting a bit of extra charge. However, this whole situation has me re-evaluating my charging strategy. I am over 20 miles from the nearest supercharger (and has often been full when I have tried to use it in the past), and the few nearby chargers which are even slightly fast are unreliable at best. In an emergency, I don't want to be scrabbling around for a charger.

My main plan is to charge higher (90%) and not let the level get so low. However, I was wondering how others were dealing with changes to their driving patterns, and whether I should even bother being so careful about when/how to charge?

Thanks in advance
 

nxsynjs

Member
Jul 5, 2020
241
191
UK
It's very much an individual calculation. Personally I always leave at least 25% as a buffer(long enough to get me to my parents and then some in an emergency) but my daily charge total kinda varies. I charge to 88% on a friday night, which is enough to see me through the weekend, then top up to 75% sunday night and from then on 52% Mon-Thurs as and when the car needs it.

The idea is to keep the car charged between 50 and 75 as much as possible to help conserve the battery. The only downside of this is that the car could need a battery balance a couple of times a year but that is more of an maximising thing than something that is needed.

I do suspect once i'm an EV veteran such details will become irrelevant and i'll just use it and charge only and to the extent it needs it.
 

Type2

Member
Jul 6, 2019
86
66
Liverpool
Personally I always have the car plugged in and at 80%
Not only does it align with Tesla’s recommendation but it also allows plenty of range for unforeseen trips.

As well as umpteen opinions on what is the best charging strategy there are umpteen opinions on what Tesla recommends.

When I picked my car up from West Drayton the Tesla employee who did the hand over told us that he had seen many posts about whether 60%, 70%, 80%, 90% or other variations were best for the battery. He stressed that 90% is what Tesla recommends.
 
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ACarneiro

Active Member
Jun 20, 2019
1,310
1,032
Shrewsbury, Shropshire, UK
As well as umpteen opinions on what is the best charging strategy there are umpteen opinions on what Tesla recommends.

When I picked my car up from West Drayton the Tesla employee who did the hand over told us that he had seen many posts about whether 60%, 70%, 80%, 90% or other variations were best for the battery. He stressed that 90% is what Tesla recommends.
Yes, I believe The Musk was quoted stating the 90% figure.
I'm being conservative :)
 

akenham

M3 LR AWD+ 2020
Sep 19, 2020
73
83
East Anglia, UK
Short answer
Like others I've spent ages agonising to arrive at the same conclusion as everyone else: charge daily to 80-90% o_O
... unless I absolutely know I'm going nowhere (e.g. a second lockdown) in which case I would probably drop to 50-60% for "storage".

Longer answer / whyso
I also do 40 miles on a typical day, consuming 15-20% of battery depending on temperature and conditions (country lanes, A roads, city roads, lots of stop start and frequently waterlogged surfaces).

Required charge level (for winter, about 1/3 less required for spring-autumn)
  • I don't want to plan to go below 20%
    -> min level 20%
  • I'll typically use ~20% per day for ~40 miles for school/work run
    -> min level 40%
  • High chance of needing a second run/errand ~20% for ~40 miles
    -> min level 60%
  • Rare but highly inconvenient events: a third errand or car fails to charge overnight (e.g. power outage) - I want to have enough for tomorrow's morning run (w/o using the <20% with reserve, so I can hit up the local supercharger or fast charger ~16. miles away without sweating it or making myself late).
    -> min level 80%
So my winter min daily charge is 80%

But... it's very hard to argue a big difference in battery life for 90% vs 80% and having more reserve in winter is valuable to me (e.g. the other day when it snowed unexpectedly and my journey doubled in both time and distance to get round problems whilst the rolling resistance over snow/slush and my cabin heat needs made energy consumption soar). It also saves me messing around switching charge levels between weekdays and weekends or having to think ahead to plan for the odd longer trip.

So on balance I'll probably leave it at 90% until spring, barring known low consumption periods (xmas holiday during pandemic) and revert to 70-80% when warmer weather naturally boosts my range (all the 20% become 14%).
 
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HenryT

Member
Jan 29, 2020
565
456
Manchester
As well as umpteen opinions on what is the best charging strategy there are umpteen opinions on what Tesla recommends.

When I picked my car up from West Drayton the Tesla employee who did the hand over told us that he had seen many posts about whether 60%, 70%, 80%, 90% or other variations were best for the battery. He stressed that 90% is what Tesla recommends.

Interesting too that the Tesla app sets the 'daily' range as between 50% - 90% and the 'trips' bit at 90%+
 

akenham

M3 LR AWD+ 2020
Sep 19, 2020
73
83
East Anglia, UK
Sitting around the 50% level is good for battery life (but diminishing returns reducing from 90 to 80 to 70 to 60...)

Shallow cycles (e.g. 60-40 rather than 80-20) are better for battery life.

Hence the recommendation of 50-90% and daily charging.

But both of these mean you give up immediately available range so depends what fits with your life and tolerance to plan ahead.

Sub-80% charge levels and shallow cycles can make the BMS estimate of range somewhat less accurate but does not affect your actual ability to drive to the full range so I don't think it's worth sweating over this factor.
 
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phil4

Member
Sep 8, 2020
294
162
UK
I've been all over the shop on this, and settled on 80% as what I try and leave it on unless going on a longer trip.

I've seen it drop to 54% on a normal commute (38 mile) when it's cold like this, and so I'd rather not drop it much lower. I'm also not so paranoid I'm worried about the difference between 80% and 70% etc... after all the car's on a 4 year PCP.
 

Jeeves

Member
Feb 12, 2020
506
285
UK
+1 for 80% every day unless I have a long trip planned.

I was preoccupied with all this stuff when I first got the car because it was all new to me. I rarely consider it now. Part of me thinks one shouldn’t need to. The other part reminds me that we are all part of the Tesla alpha test programme, I guess that’s why I’m on this forum.
 

spon88

Member
May 2, 2019
515
287
Derby
I've had similar thoughts to this, particularly in that I work from home and don't do much mileage - maybe as little as a couple of relatively short runs on a typical week. In fact I deliberately head out now and again just to enjoy the car and scrape the rust off the disks!

I've settled on 80% max unless I do have a longer trip and then let this reduce to around 55% - then I top up. The car (M3P) seems to sleep soundly and loses very little each night, so it can sit in the 70 - 80% range for several days sometimes. Hopefully this doesn't degrade the battery too much although you do see the BMS range figures fluctuating a little with a charging regimen like this - anything from 297 down to 290, depending on the ambient temp, previous SoC etc. The car is an August 2019 model.

I try not to worry about it too much these days and it pays to have a decent level of charge in case of unforeseen events like the OP experienced.
 
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Drmouse

Member
Jul 25, 2019
71
29
UK
Thanks all

What do people generally do and/or what is the advice when they are not going to be driving for, potentially, a week or more? e.g. Leave plugged in at a set charge limit, unplug, play with limits?
 

Jeeves

Member
Feb 12, 2020
506
285
UK
From the manual:


About the Battery

Model 3 has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model 3 for several weeks. When plugged in, Model 3 wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.

NOTE: When left idle and unplugged, your vehicle periodically uses energy from the Battery for system tests and recharging the 12V battery when necessary.

There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.

About the Battery
Model 3 has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model 3 for several weeks. When plugged in, Model 3 wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.
NOTE: When left idle and unplugged, your vehicle periodically uses energy from the Battery for system tests and recharging the 12V battery when necessary.
There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.”
 
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spon88

Member
May 2, 2019
515
287
Derby
Thanks all

What do people generally do and/or what is the advice when they are not going to be driving for, potentially, a week or more? e.g. Leave plugged in at a set charge limit, unplug, play with limits?
I leave mine plugged in and set the app slider back if I don't want my overnight charge to kick in. I'm not in the car regularly but charge to 80%, leave if for a couple of days and then try to drive it to drop the charge back to maybe 70%. I'll then leave it another couple of days (unless I need it), maybe have another quick drive to drop the battery level again, then charge back to 80%. I have no clue whether than is necessary/useful but it gives me chance for a quick drive now and again and also hopefully keeps the charge level in a range where degradation is limited.

I can't believe that if you left your car say at 85% or even 90% in an airport car park for a week or so would cause any real problems, but you could always stick Sentry on for a few days to drop it a bit if you were worried. But I can't give a definitive answer to be honest.

I've never seen my car start charging on its own and I suspect this may only happen if the charge starts to drop to low levels where mine rarely goes unless I've been on a long trip. Others may see different behaviour.
 

VanillaAir_UK

Supporting Member
Jun 17, 2019
7,773
5,225
Surrey, UK

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doats1

Member
Sep 11, 2020
126
85
London
I charge to 90% on a Sunday evening, and by the end of the next week I'm at 20-30%. I don't leave it plugged in, though.
 

Adopado

Active Member
Aug 19, 2019
3,602
2,720
Scotland
I charge to 90% on a Sunday evening, and by the end of the next week I'm at 20-30%. I don't leave it plugged in, though.

With such low usage you also have the option of doing some intermediate charging (if you are doing this at home) and keeping the car within a more mid-range percentage for more of the time. There's nothing wrong with doing it the way you describe but in theory your long term battery health could be even better i.e. even slower degradation. It also means that you always have a higher minimum percentage in the tank for those unexpected journeys. (I would never plan to have an ICE car sitting with only 30 miles range in the tank i.e. equivalent to an SR+ at winter temperatures with 20% battery, because it can mean an unplanned excursion to a petrol station ... and with an EV you don't even have that option unless you live near a Supercharger.) If plugged in you also have the preheating option to save range ... every percent counts in an SR+!
 
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