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Discussion Starter #1
Hi all i3 94Ah REX owners

I have a very specific question was wondering if anyone could answer.

From a 100% battery charge, how long do you think your battery would last in the following situation:
  • Car switched on, in park mode
  • Music system playing at mid volume
  • Winter with heating on mid, and low fan setting

Basically, imagine you want to use the i3 as your office for the day, in winter, and want the radio on the whole time and not get cold...how long would the battery last before the REX kicks in and saves you from being stranded?

I presume if it was summer you’d get a bit more time as I understand A/C uses less battery than heater?

Thanks
 

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The heater is going to use something like 1 to 5 kWh per hour. Depends on the weather, set temperature and how often the doors are open. I'd guess six hours worst case but usually a lot longer.

Maybe 8 hours worst case if you precondition first.


AC is less than the heater and you can usually just roll the window down.


The others are negligible.
 

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I have a very specific question was wondering if anyone could answer.
I have a very similar query - although in my case with no REX backup and because I’ve contemplated sleeping in the back (probably not in winter), and that would ideally involve climate control through the night to deal with the condensation issue.

I’ve been meaning to test it somehow - it will probably involve blocking the car in on the driveway (so it couldn’t be stolen), leaving the car turned on, climate turned on, and leaving it all day for 8+ hours.

The other issue I’d have is needing to do something about the DRLs at night - maybe just covering them with something - but the driveway test is probably what I’d do if I were you.
 

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No heat pump for me unfortunately - but I’m thinking in my case the outside temperature when I would do it wouldn’t be below about 15°C and the cabin would be set to maybe 19°C for sleeping so any benefit would probably be limited anyway.

I think the only way to confidently say how long the battery will last is to test it.
 

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The drain should be nearly linear so all you would need to do is test the time taken to get from say 95% to 85% and multiply by 10. The outside temperature will have more impact than any non-linear portion of the battery drain curve. The very top and bottom 5% will be the most non-linear areas as the battery output voltage reduces. The carbon fibre shell is a better cabin insulator than a steel one.
 

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The outside temperature will have more impact than any non-linear portion of the battery drain curve.
Yes, in the winter daytime case you could probably just test for a short time and then extrapolate as the outside temperature is usually fairly constant between, say, 9am - 5pm.

In the overnight case though, temperature is more likely to drop, and not be so constant between say, 11pm - 7am. So in the overnight case I’d be wanting to do alonger test ideally (or test during a day time period when the temperature is low and then extrapolate that to get a worst case result).

I think you’d want to be more cautious with the overnight use case as, obviously, you can’t keep an eye on the SoC like you can with the daytime use case.
 

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Discussion Starter #8
Thanks all. Perhaps to simplify my question at this stage, how long would the battery last (from 100%) if only the music system is playing at mid level volume in stationary park mode?
 

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Thanks all. Perhaps to simplify my question at this stage, how long would the battery last (from 100%) if only the music system is playing at mid level volume in stationary park mode?
With no driving or the use of heating? That would be measurable in days rather than hours. Probably more than a week.

With the heating on you'll be using significantly more power and without a heat pump you could probably deplete a full battery within 12 hours, probably even less than that if you want the car hot rather than warm.
 

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Thanks all. Perhaps to simplify my question at this stage, how long would the battery last (from 100%) if only the music system is playing at mid level volume in stationary park mode?
If the car is not in “ready” mode though it will keep turning the radio etc off after a short time (30 minutes or so I think).

If it’s in ready mode, with the HVAC system turned off and the main screen display turned off, and just the radio (and DRLs) on, then it would likely last for a very long time.

Probably using a few hundred watts at most.

I guess battery cooling / heating might kick in from time to time depending on the outside temperature.
 

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A 94Ah i3 has 27.2 kWh useable.

But you most likely wouldn’t / couldn’t use more than 90% unless parked next to a charger.

So let’s say you have 24,500 Wh to use.

Then if we say the stereo alone, plus DRLs and some occasional battery management uses an average on 200W.

Then the battery would last 122.5 hours or 5 days 2 hours and 30 minutes.
 

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Discussion Starter #12
Thanks for these recent replies. All very interesting.
What’s the difference between being in ready mode with radio on, and NOT in ready mode with the stereo on?
 

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Discussion Starter #13
also, how low would the battery get before the REX kicks in? I presume the system won’t allow it to get down to 0%?
 

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Thanks for these recent replies. All very interesting.
What’s the difference between being in ready mode with radio on, and NOT in ready mode with the stereo on?
Ready mode is only entered when you press the on button with the brake pedal pressed.

The car is then ready to drive.

‘Not-ready’ mode (akin to just turning on the ignition in an ICE car) is entered by pressing the on button without pressing the brake pedal.
 

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I haven’t tested this myself, but apparently if you did want to leave the car in ready mode (bearing in mind that someone could easily steal the car if left unattended) then you need to exit the car via the passenger door to prevent it automatically turning off when the driver’s door is used.
 

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also, how low would the battery get before the REX kicks in? I presume the system won’t allow it to get down to 0%?
This is one for the REX drivers to confirm but I think it will always come on around 8% or something like that - could be mistaken about that though.
 

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Discussion Starter #17
Thanks. No I’d never leave the car unattended. So in summary, in “ready mode” with just stereo on, we’re talking days. With stereo and HVAC we’re talking several hours, maybe up to 12 hours.
And when would the REX kick in in this scenario?
 

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Discussion Starter #18
Sorry BillN just saw you answered this, thanks! REX drivers please confirm if you can thanks
 

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Yep I think those timescales are roughy about right - but just to emphasise HVAC impact greatly depends on outside temperature vs inside target temperature.

In winter, or in summer in strong sun, you could also do things to help the HVAC use less energy - eg insulate the windows or use sun shades.
 

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Yep I think those timescales are roughy about right - but just to emphasise HVAC impact greatly depends on outside temperature vs inside target temperature.

In winter, or in summer in strong sun, you could also do things to help the HVAC use less energy - eg insulate the windows or use sun shades.
Thanks Bill. How are you finding ONTO? They only seem to have Zoe and everything else is a 3 month wait or longer :(
 
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