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What should my ideal charge percentage be?
- Thread starter Al Sherman
- Start date
E90alex
Active Member
It’s to warm the cabin. The battery may be minimally warmed more as a side benefit but it’s not the primary purpose of departure preconditioning.
Cold battery doesn’t degrade it. It might not be able to provide full power or accept full regen.
The car doesnt warm the battery unless its sbout freezing, and in that case only to about 5C above freezing.
Warm battery is performed by charging late with max available power.
Nope.
The degradation during cycles is lowest at about 25-35C cell temp, but not at all *bad* below.
If the battery is below sbout 3C the car active warms the battery very quick to about 5C or so.
Cyclic aging is low anyway. The little increased wear from low cell temp is more then well compensated by much lower Calendar aging.
So warm battery is only beneficial for performance and we want the charging to end around the same or before we start driving?
I start charging at 12AM for rates at home and it would be done much earlier than I hot the road. Also I might never hit the road the day after.
Should I try to start charging even later than 12AM to synchronize with departure?
And if I cannot do this and keep doing 12 AM and somedays even not charging at all, it won't hurt since this is only for performance not for battery degradation anyway?
E90alex
Active Member
If your TOU window ends much before you leave then just charge when it’s cheapest. But if you leave at a consistent time everyday then consider changing to departure off peak charging instead of having it start charging at 12 am.
Completing charge right before departure is more for efficiency than battery health.
Also once a while should I charge to 100%? (or anything between 100 and 55, if I keep doing 55%)Is there any benefit?
My 75's battery: I did always charge to 90% and now I started to charge it to 70% 80%. I did not know about the complexities of batteries other than not charging 100%. I only charged to 95% for a couple road trips.
For the new car I will try to follow what I read here . The big difference is I supercharge the old one meanwhile the new one is only charged at home with max 30AMP slow charger. Would that be a problem?
My 75's battery: I did always charge to 90% and now I started to charge it to 70% 80%. I did not know about the complexities of batteries other than not charging 100%. I only charged to 95% for a couple road trips.
For the new car I will try to follow what I read here . The big difference is I supercharge the old one meanwhile the new one is only charged at home with max 30AMP slow charger. Would that be a problem?
Ok, now that we have our car back from Tesla warranty service, it seems I was confused by our charge screen. As others have suggested, it only says "80% recommended for daily driving" when I move setting for "charge from solar" above 80%. We never set the normal charge that high, and for two years we kept our 2021 Model 3 at 70% except when leaving for a road trip. So, we'll just go back to a similar regimen, and won't set the opportunistic "charge on solar" feature above 80%. Mystery resolved.
When not driving, the colder the better fit the battery.
When driving, warmer is slightly better than colder so 20-35C is the optimum. The difference is small enough to be eaten by increased calendar aging.
For low rates and stuff you need to figure it out for your self. The compromise between cheap and low degradation can only you weigh.
At winter or colder times, a recently charged battery (preferably with high power) will be warmer and that heat can ve used by the heat pump to heat the cabin.
The difference can be considerable.
In -20C after a Supercharging I drove highway AP speed at about 185 Wh/km in one direction. On the return the battery was cold. Still same temperature, same speed and road at sea level, and absolutely no wind I had 260Wh/km on the other way.
Thats the extreme but from homecharging the battery heat can be useful for about 30-60 minutes of driving at sub freezing temperatures. Still considerable difference in consumption so when counting the beans, you can use the heat loss you paid for when charging if cold outside. 1 kWh heat loss in the battery is worth about as much as 1 kWh in the battery.
This is a shame that app is gone.
BTW should I ever charge to high percentages for the health?
Nope, not helping the battery with that.
But there is no reason not to charge to high SOC when needed, and you should not be afraid to use all of the battery if needed.
Theres a lot of talk about BMS-calibration and bringing back range. It doesnt bring real capacity or real range, it brings displayed range back.
But if the BMS is severely of, a BMS calib can make the navigation calc better as it knows the real capacity of the battery.
My MSP BMS was severely of when I got the car (or after a 1000km delivery drive home). the BMS showed 95.3kWh out of 99.4kWh. It was quite easy to calculate the real capacity (I have described this on TMC in a few posts). I did not perform a BMS calibration, but I just used the car as needed and it adjusted itself after about one month.
The only thing charging to 100% does is calibrate your BMS. It does not magically make your car drive farther. Maybe once a year I go on a long enough roadtrip to really do a proper calibration. To really get clean numbers ideally you would get to 100%, then drive it down to ~10% (or lower) and then charge it back up to 100%, then back down again. As mentioned I can only justify doing this on road trips. Some say just put it up to 100%, let it sit for a hour or so to really balance the cells, then drive it down under 90% and you're fine. I don't often deep cycle the battery, but when I do its only to get a good battery calibration. 2 passes of 100% charge back down to single digit % and back to 100% is enough to get the BMS adjusted.
Honestly doing it like that isn't very good for the battery, which really is why I only do it once a year (if that). Then for the remainder of my trip I'm back to shallow charges at the low to middle of the pack.
Hi, sorry to bump this up, but after reading many pages I am not clear -- so many different recommendations. for an original P85 (battery replaced with a new one 5-6 years ago), what is the best method to prolong the battery?
I see references to 50-55%, but that means charge to that as max and how low is too low?
If anyone can summarize the current thinking I would greatly appreciate it.
I see references to 50-55%, but that means charge to that as max and how low is too low?
If anyone can summarize the current thinking I would greatly appreciate it.
80% has always been the standard for longevity regarding battery life
E90alex
Active Member
Lower SoC is better overall for degradation. Set your charge limit to as low as you can while still meeting your usage needs. Below ~55% is best if that works for you.
There is no “too low” SoC unless it’s fully dead, which is damaging to the battery cells. But the car will turn off before it gets to that point. There is no harm in running to below 20%, 10%, or even 5% if that’s what you’re asking.
There is no “too low” SoC unless it’s fully dead, which is damaging to the battery cells. But the car will turn off before it gets to that point. There is no harm in running to below 20%, 10%, or even 5% if that’s what you’re asking.
I am in Canada and during the winter I want my charging to end at 7 am as that is when my electricity low price ends and that is a bit before I leave home. When the ambient temperature is low it is better to have a nice warm battery so you don't have limited regen. But I don't imagine that is an issue in San Diego very often, Toronto is a different story.
geordi
Mr Fusion V.1
For a classic Tesla (pre-2019 or so) or any with the same lithium ion battery, keeping the battery between 70% and 20% for daily use (or maybe a bit less on the top end if your daily mileage can support that) is best.
What MOST affects degradation: High temperatures!
Storage / not driving it after charging it up to very high (over 90%) levels and not driving within an hour or two also hurts the battery.
Storage / not driving with very low charge levels, ALSO at high temperatures as a contributing factor, will hurt the battery.
Daily use in as narrow a band as reasonable, with the upper end as low as possible, will protect the battery. BUT - we are talking about a difference in degradation of only a few percent over time, so the main thing is just this: Use the car and enjoy it. You will get the best battery life when it is being used, rather than just sitting at any charge level. Age degradation will happen no matter what.
I don't have the same battery as you do (23 MSP), but my takeaway from this thread according to graphs that are beyond my comprehension is that for battery preservation around 55% is optimal. I however charge to 59% figuring that it won't make much difference. Why 59%? Because it gives me exactly 200 mile range. I don't actually need that much range on a daily basis, but the OCD considerations the necessitate a round number are strong. 
I don't always wake up to that number ... sometimes it's a mile or two above, sometimes it's a mile or two below, but every once in a while I wake up to exactly 200 mile range showing on the app. Oh what glorious days those are!
I don't always wake up to that number ... sometimes it's a mile or two above, sometimes it's a mile or two below, but every once in a while I wake up to exactly 200 mile range showing on the app. Oh what glorious days those are!
I have a 2014 Model S P85D. I have always set the charge limit to 90%. A few times per year I will do longer trips and charge to 100%. I don't drive a lot - my car only has about 110,000 km in that time. My battery has lost about 5% if I can believe the car's range reporting. Initially I had 400km of range when the battery was at 100%, now I have about 380km. I don't baby the battery.
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