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Should I charge now or ok to wait for off peak??

I just completed my first long trip in my M3P. I ended up getting home with 9% battery and as soon as I clicked into park I got a message saying, “Battery very low so not idle and charge now.” I plugged the car in and went inside. I set my charging to take place during off peak hours. My question is, do I take the car literally and begin charging now or is that just a warning to find a charge spot if your still driving? Am I ok to wait for off peak or is it best practice to just start it now?
 

Tam

Well-Known Member
Nov 25, 2012
11,269
10,308
Visalia, CA

I would feel more comfortable delaying charging and waiting for the cheap time if I have around 20%.

The problem of waiting while your battery is low is: when it's cold weather, your battery level will continue to get lower because your battery will no longer be hot but it will cool down (more range when warm and less range when cold).

If it gets to a certain low level, the main battery will not allow draining anymore and it will not charge the 12V battery.

I haven't experimented with delaying charges when lower than 20% so your 9% might be fine as a good trial and error.

The worst would be your car acting as if it's dead when it's time to charge at the cheap time: Can't open doors, everything is dark... but don't worry, just manually open your frunk and inject 12V to the 12V battery and it would wake up again.
 
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I will also add that I will be making the same trip again tomorrow. I normally charge to 80% daily. For todays trip I charged to 90%. Tomorrow I will try 95% just so I don’t end up so low when I get back home. I set the precondition and off peak charging so it finishes and I leave at the same time.
 
Found this too;

Note
Whenever Model 3 is plugged in but not actively charging, it draws energy from the wall outlet instead of using energy stored in the Battery. For example, if you are sitting in Model 3 and using the touchscreen while parked and plugged in, Model 3 draws energy from the wall outlet instead of the Battery.

Seems the battery should not lose any charge while plugged in.
 

Tam

Well-Known Member
Nov 25, 2012
11,269
10,308
Visalia, CA
...should not lose any charge while plugged in...

My expensive peak charging time is 4 to 9PM so I schedule my charging time as 9PM. If I arrived home by 4PM, it won't charge any until 9PM. That means the car would continue to lose its range until it's charged back up again at 9PM.

So at 4PM, I can be a DJ and blast the music, thump the bass loudly, but the car won't charge up until 9PM. You know that it doesn't use the shore power because the HPWC light doesn't flash.

However, it does use shore power for HVAC. You know that it's using the grid power for HVAC because you can see the HPWC light runs up and down.
 
  • Disagree
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Tam

Well-Known Member
Nov 25, 2012
11,269
10,308
Visalia, CA
...I will try 95%...

Oldie but goodie 2013 Charging Guide: If you have to choose: 100% or 0%, choose 100%:

 

drtimhill

Active Member
Apr 25, 2019
3,213
4,189
Seattle
I just completed my first long trip in my M3P. I ended up getting home with 9% battery and as soon as I clicked into park I got a message saying, “Battery very low so not idle and charge now.” I plugged the car in and went inside. I set my charging to take place during off peak hours. My question is, do I take the car literally and begin charging now or is that just a warning to find a charge spot if your still driving? Am I ok to wait for off peak or is it best practice to just start it now?
Charge to 20% for peace of mind but a few more $$ .. then do the rest on your normal schedule.
 
There's a bunch of info out there about keeping a healthy BMS - you can google it if you want. Long story short, BMS won't re-calculate battery capacity until voltages stabilize in the pack. For the M3, it can take hours before that happens (versus minutes in the S apparently).

So, it's actually good when your battery is really low like that to wait before recharging so your BMS can "learn" where the bottom of the battery is. It should result in more accurate battery capacity calculations.
 
I like this idea. Going to charge up to 20% then cut it and finish up during off peak
Be nice if Tesla could make that auto-magic. The max power usage would be around 14KW to get to 20% SOC. Now with our on peak summer rate of over 50 cents that could add up. Our summer peak time is from 1PM to 6PM so I would probably take the chance and wait until after 6PM.
 
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brkaus

Well-Known Member
Jul 8, 2014
8,578
7,198
Austin, TX
Why is this viewed as "taking a chance"? The car is safely sitting in a driveway. It is not going to be subject to anything like hard acceleration that would pull the battery low. If it does continue to use battery for cabin overheat, etc... it won't leave someone stranded.

Sure, it has a warning that pops up... and that is helpful if one is out driving around and expects to come back to a car charged at the same level they left it if they go shopping or into the office...

IMHO - this is pretty much a non-issue. No way I would spend peak power if I was sitting at 5% or more and not planning on going anywhere. I'd plug the car in and let it start charging at it's scheduled time.
 
I will also add that I will be making the same trip again tomorrow. I normally charge to 80% daily. For todays trip I charged to 90%. Tomorrow I will try 95% just so I don’t end up so low when I get back home. I set the precondition and off peak charging so it finishes and I leave at the same time.
If you know you're going to come back that low, charge to 100% before you leave. I also agree that leaving it at 9% for a few hours is meaningless. It doesn't pay to get too paranoid, especially on things you don't do daily.
 

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