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Minimum charge

JulienW

Active Member
Jul 7, 2018
4,242
6,395
Atlanta
There are no absolute numbers that are best or worst for lit-ion but.....the less time spent at a lower or higher state of charge the better. A general good rule of thumb is the 20%-80% rule. If charging higher than 80% or discharging lower than 20% spend less time at those states.
 
If you think the battery needs to be cycled you are wrong.
The 90% suggested charge is about making sure BMS (battery management system)estimates of charge level are accurate. From a pure battery health perspective it is completely unnecessary.

Far as discharge level plug it in daily and charge to 70-90% whatever the discharge level is is fine so long as you aren't spending a lot of time below 10%. If using 5% a day you can replenish that daily or if you use from 90 down to 10% a day that is fine too, and on trips don't hesitate to tap into the top and bottom 10% just don't let the battery spend a lot of time there.

When I mentioned the BMS estimates the deal there is battery voltage is very stable in a range from something like 10-90%, if the pack is charged to 70% daily the BMS can only estimate charge level based on measurements of input and output. Reason Tesla suggests 90% is because that gets to a point where cell voltage begins to rise giving BMS a measure of real time charge level rather than just an estimate. If limiting peak charge below that you can see range estimates creep down, this is not loss of actual capacity just BMS calibration error which can be reset by letting charge go below 10% and then charging to over 90% so the system can measure voltages at those extremes and find its place again.
Tesla recommends keeping the car plugged in at home because then it can draw from the outlet as needed rather than discharging the battery some thereby reducing discharge cycles on the battery.
 
Far as discharge level plug it in daily and charge to 70-90% whatever the discharge level is is fine so long as you aren't spending a lot of time below 10%. If using 5% a day you can replenish that daily or if you use from 90 down to 10% a day that is fine too, and on trips don't hesitate to tap into the top and bottom 10% just don't let the battery spend a lot of time there.

I disagree with the part about constantly staying in a high SOC being OK. Based on the information about general lithium battery chemistry, if you are only using a small portion of the total capacity of the battery, ideally you want to keep the average SOC near 50%. So charge to 60% if you're only going to use 20% before you charge again.

Now, I agree that the above doesn't account for BMS calibration. So, IMO, if you're going to do what I just suggested, you'd want to charge up to 90% at least once every couple of weeks to keep the BMS happy.
 
I understand the high state of charge being bad argument, since Tesla says set it to90% and keep it plugged in I really don't think it is that bad.

I will admit I keep my S at 70% in fair weather and at times go a few days between plugging in but come winter it is 90% nightly. Winter here near Green Bay is real and dramatically increases energy use.
 
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I understand the high state of charge being bad argument, since Tesla says set it to90% and keep it plugged in I really don't think it is that bad.

I will admit I keep my S at 70% in fair weather and at times go a few days between plugging in but come winter it is 90% nightly. Winter here near Green Bay is real and dramatically increases energy use.
Hi
i am in the UK so weather in winter nothing like you but out of curiosity as i am new to EV - you say battery consumption far higher in winter - is that due to using heaters moe etc or is consumption higher due to car working harder etc?
just trying to learn all the quirks of EV's
thanks
 

JulienW

Active Member
Jul 7, 2018
4,242
6,395
Atlanta
Hi
i am in the UK so weather in winter nothing like you but out of curiosity as i am new to EV - you say battery consumption far higher in winter - is that due to using heaters moe etc or is consumption higher due to car working harder etc?
just trying to learn all the quirks of EV's
thanks
Mainly the heater working. Also the battery has to be heated some too. Use the seat heaters and keep the cabin temp a little lower and this will lower consumption.
 
Hi
i am in the UK so weather in winter nothing like you but out of curiosity as i am new to EV - you say battery consumption far higher in winter - is that due to using heaters moe etc or is consumption higher due to car working harder etc?
just trying to learn all the quirks of EV's
thanks
Heating, cabin, seats and the pack, my car has seen -30c.
My commute is short at 6.5miles each way, which means either I need to preheat well in advance which uses power from the outlet or the heater is running hard the whole drive. If good and cold energy use can triple for the first few miles, as the cabin warms consumption falls back nearer normal. The effects of cold are less prominent if you are going on longer trips because you are warming the cabin just once.

The instant heat is amazing, I start because no waiting for an engine to warm up.

You don't see it in use but the pack must be warmed to charge so that raises the electric bill some as well.
 
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Reactions: poolmeds

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