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Technical battery question------need help.

Technical battery question------need help.

Hi Guys,

I'm the only guy at work in line for a M3 on my crew. I work with 25 hard core ICE drivers. Today one of the "other" guys asked me this question.

"If you leave your car in a warm garage for weeks on end, will the battery slowly loose charge ?" What I told him was, that I was not planning on driving it, in the Winter months. This seemed like a fair question to me. I would also like to know the answer.
I know many of you can tell me what the answer is. So.............. I'm listening.

Bob in Seattle

KP in NPT | June 1, 2017

Yes it will lose charge. If you were worried it would lose enough to drain the battery completely, you would simply leave it plugged in with the charge limit set to whatever you wanted.

KP in NPT | June 1, 2017

The model S and X, and presumably the Model 3, have an energy saving mode that will reduce "vampire drain." You would enable this mode if you knew you would leave the car parked for an extended period. But best practice if you plan on leaving it parked for weeks is to leave it plugged in.

Even without this turned on, the car will go into a "deep sleep" after a couple/few days which reduces drain. If you didn't leave it plugged in, you would want to at least monitor your state of charge via the app to ensure you don't drain the battery completely.

ReD eXiLe ms us | June 1, 2017

'Tesla Model S vampire drain after 27 days in winter' -- Bjørn Nyland

He left his car in Norway while he went to Thailand to get married.

[ YouTube -- JEPBkjmS2uE ]

jsanford | June 1, 2017

I'm assuming the charger has a "battery tender" mode.

msmith55 | June 1, 2017

The main Thing is the temperature, if its above freezing then the battery will probably not be damaged by low charge if plugged in, but if the temperature is below freezing, like -20 F, even a level 1 (110 V, 15 A charger, 2.2 Kilowatts) may not be enough to protect the battery. The battery heater uses 6 kilowatt, intermittently, and if the battery goes completely dead it will be damaged beyond repair. You need to use a plug in charger with capacity over 6 kilowatt for freezing weather! A level 2 charger at 240 V, 30 Amp or more will work.

bernard.holbrook | June 1, 2017

That's a lot more drain/heating power than I expected. It's something I will keep in mind.

Thanks Red and msmith.

Captain_Zap | June 1, 2017

As your car sits for longer periods of time, the car consumes less power. It goes into a coma-like state and it will be slow to wake up. The car tries its best to protect itself.

stevenmaifert | June 1, 2017

@msmith55 - 6 kW or 6 kWh? If the battery heater draws 6 kW, for how long does it draw that power? You said the draw is intermittent. If a heating cycle uses 6 kWh per cycle, and the cycles are more than 3 hours apart, a L1 charger will replace the power consumed during the time between cycles.

To answer the OPs, question; yes the battery will slowly lose charge even in a warm garage because there are "things" running in the background that consume a small amount of electricity even when the car is sitting idle. We don't yet know how many of those "things" the M3 will have, but some of them will likely have a use or don't use option on the touch screen, and there will likely be a power conservation mode that powers the car down to a lower state of readiness when idle but then takes the car a little longer to "wake up" when you get in to go somewhere.

Bighorn | June 1, 2017

BMS activates battery heating, drawing 6kWs to maintain threshold temperatures. Vampire drain is usually less than 100W and decreases with time. What's nice for the OP is that one usually has a ready replenishment source in their garage and it's suggested the car stay plugged in.

I trust your friends are aware that gasoline evaporates readily, moreso in the summer and depending on the blend.

dd.micsol | June 2, 2017

Car is in sleep mode like a computer. yes there is trickle draw and charge if plugged in. It's power use is similar to that of a latitude d630 or 30w/hr. If you program the charging-it will take the majority of the draw to charge the battery pack during those hrs.

shepbob | June 2, 2017

I question the premise of your question. I think you are dreaming if you think leaving your Tesla undriven in the Winter is going to happen.

Once you drive your Tesla, having it sit idle is about the last thing you'll want to do! ;)

bj | June 2, 2017

It definitely will not loose charge. The electrons will remain tightly bound.

tstolz | June 2, 2017

+1 Shepbob ... I was just about to post the same thing!!

jforbes77 | June 2, 2017

So if I left my Model S in a underground parking for a week with a full charge, what would be the charge level after a week?

DTsea | June 2, 2017

Jforbes full charge is never recommended for a car parked a long time.... only for when you are driving right away. When idle 80% or so is better. You will only lose a few percent in a week.

gatorj31 | June 2, 2017

I think I read somewhere that trickle charging the battery isn't as good for the battery as using a level 2 charger. Does this sound right? I currently have a LEAF and a level 1 and level 2 charger. I've always kept the LEAF plugged into the trickle charger as I assumed slower is better. Thoughts?

DTsea | June 2, 2017

Gatorj31, you cannot trickle charge a Tesla. When you leave it plugged in, every few days when the vampire drain causes a decline big enough to trigger charging (seems to be 5-10 mi rated range, 4-5 days) it will charge at whatever amp level you set for normal charging (ie after you drive the car). No slow constant trickling.

TeslaTap.com | June 2, 2017

To expand on DTesa's excellent answer, you could use a 120 VAC outlet (12 amps) or L2 charger (240VAC, 30-40 amps). The only difference would be the "on" time of charging would be longer with the lower power. Both would work fine for an indefinite period to maintain the charge level you set. It may be slightly more efficient to use L2, but it's likely in the noise and not important.

georgehawley.fl.us | June 2, 2017

Just as an example I left my Model X in an airport parking garage for 8 days. When I returned, the number of rated miles of range remaining had decreased by 7 miles. This was in Florida so the battery did not need the climate control system to run. If you leave your car in an unheated garage in the winter, as stated above, just leave it plugged in to any outlet. It will maintain itself at the charge level that you have specified. 80-90% is typical.

JAD | June 2, 2017

Tell your friends you can leave your Tesla a lot longer then they could leave a modern ICE and expect it to start.

KP in NPT | June 2, 2017

+1 JAD. Both our MS and our ICE sat outside for 5 or so days after a mini-noreaster followed by single digit temps - MS started fine. ICE battery was dead.

johnse | June 2, 2017

@msmith55 "The main Thing is the temperature, if its above freezing then the battery will probably not be damaged by low charge if plugged in, but if the temperature is below freezing, like -20 F, even a level 1 (110 V, 15 A charger, 2.2 Kilowatts) may not be enough to protect the battery. The battery heater uses 6 kilowatt, intermittently, and if the battery goes completely dead it will be damaged beyond repair."

Your analysis is flawed because you are forgetting that you have a freaking huge battery. At Level 1 (which should be derated to 1.4kW when plugged into a 15A socket) during the time the battery heater is on, it would draw 1.4kW from the AC line and 4.6kW from the battery. So for any time heating (Th) the battery will lose 4.6kW*Th stored energy. During the rest of the time the battery is charging (Tc) and will gain 1.4kW*Tc energy. Tc = T - Th, where T is the total time plugged in.

To stay just at a "constant" average charge, one can then say that 4.6Th = 1.4kWTc (omitting the kW units for simplicity of notation).

4.6Th = 1.4(T - Th)
4.6Th = 1.4T - 1.4Th
6Th = 1.4T
Th = (1.4 / 6)T = .233T

Therefore, as long as the Time spent heating is less than 23% of the total time, it will do just fine using an L1 charger. My guess is that the ratio is significantly less than that unless you're talking about winter at McMurdo Sound :)

bj | June 2, 2017

@JAD - I know someone who has a second home in France and puts their Nissan Leaf into hibernation for 9-12 months when they are not there. They charge the drive battery to 60%, disconnect the 12V battery, and leave it in their garage (temp range about 5 to 15 deg C). When they come back they reconnect the 12V battery and say the charge in the drive battery has never gone below about 40%. They recharge the car, and it starts every time without a hitch as if a day had not gone by.

Try to do that with an ICE!

Earl and Nagin ... | June 3, 2017

The biggest problem you'll have with parking and batteries is if you keep an ICE around. You'll need to get a battery keeper for it since, once you have a Tesla, it will get neglected and its starter battery will be flat when/if you need it.