High voltage battery discharged to 0% by itself

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Post by betonos »


I left the car for 2 weeks with charge around 50% on the SOC (edit: maybe it was less, 30-40%?). The temperatures were 0-5C for the first week and around -1C for the second week, the car was parked outside. When I came back the car has shown 0% charge! This never happened before but this is the first time I left car for 2 weeks (previouy it was a week at most). Is this normal? Is this because of the temperatures? I’m a bit shicked and worried. Hopefuly no damage to the battery…
Last edited by betonos on Sun Jan 29, 2023 9:47 pm, edited 1 time in total.

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Post by betonos »

After 30mins of charging with the 230v charger it still says 0%. I believe this might be due to the fact that 0% is not actually 0% but perhaps 5 or 10% and therefore now it tries to gain this beyond 0 charge and will go upwards of 0 later. Will check in another hour or so… also the temp outside right now is -5C so maybe it still needs to pre-warm itself.
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Post by betonos »

An hour later, still 0% remaining, 15hrs to charge.
And about 1.5-2 hrs later it’s now at 2% so gaining visible charge now.
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Post by londiniumperson »

That's a concern that it dropped at least 30% in 2 weeks.
Not only have I not heard of this before, but here in the UK have never noticed any significant SOC reduction by leaving my car in sub-zero temperatures.
Though EV's do charge very slowly at the extremes of SOC, whether that's near zero or 100%.
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Post by MaXPainT »

Does the car have a scheduled preheat (or there is a chance that it gets enabled via the remote/app)? Preheating in these temperatures takes about 5% of your charge so it is possible to completely drain the battery within two weeks of preheating and not driving.
Is the heating on when you are charging the car? 230v charger cannot support charging and heating at the same time, therefore, if the heater is on you won't gain any charge.

A have not noticed any charge loss if the car sits outside without the scheduled preheat. So to answer your question, this is not normal.
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Post by betonos »

No, there was no scheduled preheat. The car was unplugged at the time also.

Normally I don't notice any discharge too. This was the first time I've left it for such long period. Now I'm just wondering: Tesla says it's normal for Tesla to loose 1% charge/day even if not used. And they say it may vary under weather conditions (esp. cold). If similar situation was with Honda e, I could for example assume the following:

2% loss / day (b/c of cold) * 15 days = 30% loss => battery depleted

and during shorter periods (for example not using the car for 3 days) one could even not notice the 1-2% loss/day: you leave the car with 68% charge and return after 3 days with the car holding 62% charge and you simply don't notice remembering it just to be in the 60% ballpark of charge.

Or maybe it was some bug.
Or maybe it was trying to heat up the battery even if not plugged in (which I believe is not true, it heats only when plugged?).
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Post by milligoon »

I wonder if you had charge schedules set although you weren't plugged in and charging, maybe it wakes the car up each day thereby losing some power?

Left my Honda over xmas new year period 2 1/2 weeks and not a single percent loss indeed it went up a percent as the day I went to charge it it was basking in the winter sun.
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Post by EEEE »

I have observed some of what you describe.

Certainly the charging when the HV battery is very cold is delayed. I believe that when the car is plugged in, only battery warming will take place initially before charging even starts. I observed this using my hypervolt charger and a works charger where the app shows the charge rate. The profile did not look like normal. This was in December when we had the very cold weather persistently for many days (south of the UK).

On the very coldest days (below -5c consistently) I left the car at work overnight (works christmas drinks), and then charged the following afternoon (so the pack had plenty of time to cool down from my morning trip in to work the day previous). The charger showed 2x 10 min buckets at the full 7kw, then the rate dropped down to about 3kw, and gradually built back to 7kw over an additional 40 minutes.

I suspect that when the HV battery sustains ambient temperatures below 0 for many days, and the car is not plugged in or used (to attain heating/charging), it will self heat to prevent freezing HV battery. As I understand it , a frozen battery cannot be charged at all. One or 2 day swings in the ambient temperature are not enough to deplete the thermal mass off the battery which weighs hundreds of kilos and is further packaged/insulated by coolant.

Charging/driving the car heats the battery up, so I suspect funny business is only observed after several days of cold weather and lack of use.

Perhaps our colder European owners can comment further?
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Post by betonos »

Ok, I’ve now had chance to see how it goes in a bit warmer temperatures. I’ve left the car unplugged and unused for 8 days. The temperature range was 5C (nights) to 20C. Some nights warmer, some days cooler. There was definately no need for the car to heat the battery etc. When I left the car, it was 74% SOC. When I returned it was 56% SOC. So, around 2.25% SOC lost per 24h.

If any of you have chance to measure it with your cars, that would be helpful to check if this drain is for every car similar. I believe over single night it’s inpossible to observe as you are going to loose probably 1% or sth. And it might not be linear.
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