charging overnight

charging overnight

I charge my car every day over night. I start charging when I come home, at around 7 PM the carge is complete and I can see a range of 241. I leave the car plugged in until I start in the Morning around at 7 but AM and the range is just 237. So it does not matter if I disconnect the car or leave it plugged in. Will the battery replenished never or does it start charging again after a certain time or charge loss when plugged in?

DouglasR | 1 March 2013

If left plugged in, the battery will periodically top itself off. I don't know the interval, but I suspect it is at least once every 24 hours. It will also top itself off if the charge level drops below a certain point due to the car's using its electronics. Again, I don't know what that point is.

docdac | 1 March 2013

It seems like the charger comes on and starts 'topping off' the car if I run my cabin heater for a few minutes (from the iPhone app). This conveniently warms up my battery on these 25 degree mornings in my garage.

Brian H | 1 March 2013

That is such a great connection, one wonders if it's programmed in or just a consequence of drawing the SOC down.

drp | 1 March 2013

So if you go out at 625 am and change it to max charge and then shower and leave at 7am will it charge over say the 85% to something higher, but less than say 95% and therefore not accelerate degradation of the battery but give more range?

GLO | 1 March 2013

We asked about this at the service center one day while charging our car. They indicate that during the night the battery will discharge a bit and recharge so you often get a varying amount of charge in the AM when you happen to disconnect. It's just a timing thing and nothing to worry about. We've noticed it most mornings with a range of 187-215 miles on our 60kw battery on standard charge.

Brian H | 2 March 2013

Or set the charge rate at 625 down low and cabin heating on. Very few or no miles will be added by the time you leave. But the battery and car will be warm and regen etc. will work.

gasnomo | 2 March 2013

I have specifically asked about this. My car charges to 240 (85kwh battery set to standard, not max charge) and then drops to 323/324 over night. According to Ownership Experience, this is caused by 2 things assuming your garage isn't 'cold':

1) the computer 'mistakenly' recalculating energy required to bring the battery up to temp and
2) the car will allow the battery to lose roughly 8 miles of charge before it starts recharging.

I was told that #1 is being addressed in the next software update.

Brian H | 2 March 2013

Typo? Converting miles to km without telling us? 323/324 is not a "drop" from 240.

peahl | 2 March 2013

This tread is not about a drop it is about when (time or % or miles) does the battery will be topped off when car left plugged in after initial charging to full. I am trying that this weekend (now 17 hours plugged in after initial charging to 241 miles, and the miles are now at 235)

Brian H | 2 March 2013

Someone suggested that it holds at storage levels, and does not actually top off when refilling from vampire load mileage loss. Try and track it and graph it.

jbunn | 2 March 2013


2 is important. Engineers want a bit of room between the upper and lower limits. Imagine if the time to stop charging, and time to resume charging were set to the same number. The charger would repeatidly cycle on and off, wearing out the realay.

The thermostat in your house operates in exactly the same way. Upper and lower control limits are set a degree or two apart and are often configurable.

gasnomo | 2 March 2013

sorry, yes typo, mean drops to 232/234...

to answer pahlemann, what i was told on the OE line was after it loses 8-10 'rated' miles, it will charge again...

Brian H | 2 March 2013

Some reported losses of 50+ miles. The fixed 4.2 "sleep" function is urgently needed, I think.

bfranks273 | 2 March 2013

Somewhat related, set the charge rate to something low so it charges continuously over night. It will take a little estimating math but you can figure it out with T&E. Benefits are you will have a full charge in the morning, if you get the rate right. The bulk of the KWHs will be during the morning hours of low cost, only helpful if you are on a rated plan. And the battery will be somewhat warm and you will have less or no regen restriction if you are in a colder climate.

Make a chart, like if when you come home you have 160 miles left then set it for 30 amps to have it just fully charged by morning. If you have 200 miles then set it for 20 amps. These are bogus numbers, the actual calculation is left as an exercise for the student.

peahl | 2 March 2013

So I found out when it does start charging again when plugged in all the time after a full charge, it was exactly when 10 miles were lost (not at a certain time, 24 hours like DouglasR suspected) in my case about 26 hours after the last full charge.
My question now is answered. Meaning when I will park long time at the airport (longer than 20 days) I have find to a lot where I can plug in the car for the whole time.
No more reply necessary.

StefanT | 2 March 2013

Since my S is in storage patiently waiting for me to return, the phone app has allowed me to monitor the charging cycle fairly carefully. The car is set to standard charge, plugged in continuously (110V) with the ambient temperature between 52 and 61 degrees and not driven. Once the charging reaches 240 rated miles it stops charging. The parasitic load reduces the range such that in 26 to 30 hours the rated miles drops to 230 when the charger typically kicks in again. It starts charging at only 1 mile/hr for about the first hour before it ramps up to 3 miles/hr until it reaches 238 or 239 rated miles then it drops to 2 miles/hour. I had on one instance the charge drop to 227 miles before charging started and on a couple of times it hit 228 miles.

gasnomo | 3 March 2013

Thanks for the feedback. Jibes with what the folks on the OE line have said.

gasnomo | 3 March 2013

Thanks for the info, and to be clear, I wasn't making a criticism at all, just pointing out what I was told. :) But that said, I have Nest thermostats all over my house, so they work a bit differently...supposed :).

I actually think its great they allow users to set the charge to a point where it doesn't max the battery out for the sake of extending the life of the battery.

mdtaylor69 | 3 March 2013

I have had my P85 for a week and noticed the owners manual says the batter should discharge at 1% per day when not in use (page 25). I notice that the battery is losing 1 mile per hour overnight after charging to 241 miles range on my 40 amp connection. I also lose about 10 miles range while parked at work. Is there a software setting causing me to lose 10% battery per day? At that rate, it will be hard to go away for a long weekend and still have enough juice to get home. The garage temperature is between 55 and 65 degrees.

gasnomo | 3 March 2013

i can report i see the same discharge patterns for my 85...unless its cold (32-degress and below), in which case the battery seems to lose 3-5 miles/hour when parked AND not plugged in. To answer your question though, I was told by multiple people on the OE line that the loss we are seeing overnight is part of something being addressed for the next release and relates to temp of the battery and the computer determining how much energy is required to bring it back up to operating temp...

Carefree | 3 March 2013

@mdtaylor69 - it is a known issue. Tesla released an earlier update to eliminate the "Vampire Load" and while that actually worked it created too many other issues with the car and they retracted those changes with the current firmware release.

We all expect Tesla to figure this out and put the car into "deep sleep mode" to eliminate any unnecessary energy consumption. Hopefully with the next release.

docdac | 3 March 2013

My estimated range fell from 236 last night after full charge, to 226 this morning (while plugged in). (Garage temp about 25 deg F). So, I used the iPhone app and turned on my cabin heater. After 2 minutes, est range falls to 225, after 4 min to 224, and after 6 min it falls to 223 miles. However, the charger came on at that point (6 min after turning on cabin heater). For the first 15 minutes, it drew full amperage (I have it lowered to 24A) and simply 'heated up' the battery. Estimated range had 'recovered' to 225 miles. Then, after 15 minutes, it started charging the battery (indicating 1 hr 35 min remainging). So, I conclude that turning on the cabin heater with iPhone app for 15 min will (partially) heat the battery, without putting on a charge.
My next trial will be to repeat this when it is NOT plugged in over night. My hypothesis is that the cabin heater will begin to 'heat up' the battery almost immediately after turning it on, with estimated range falling at a diminishing rate, allowing me to have an effective 15 min battery preheat without much decrease in est range. Useful for recovering the Regenerative Braking while parked on cold days.

nickjhowe | 3 March 2013

@pahlemann - may be very temperature dependent, but during my last trip the car quickly settled down to a 0.4 miles per hour loss and held steady at that for four days. Was parked at Miami. 70's during the day, 50's over night.

The next software update will hopefully bring it down to c. 0.1 miles/hour.

nickjhowe | 3 March 2013

Here's the data: