[josephraj]

Strange issue today. I had parked the car at 45% and couple of hours later when I switched on it was at 20%! Home was 24km away. Reached with 12% remaining but 25% drop for no reason is scary!

A week ago, I had stopped the car at 52%. After a few hours, when I started the car it showed 6%, connect charger! I restarted the car and percentage was back to 52%!

Not sure, if I have a battery issue. Car is less than a month and 2000 kms old

[Sentinel17]

Not an expert or anything
But TATA cars are known to have electrical issues.
Here,it could be a faulty sensor.

[srini1785]

I am not a EV battery expert but here goes my 2paise.

In our mobiles, there is a battery management system and time to time you need to calibrate your battery management system. By that I mean that you have to let your mobile drain all of the battery till it is 0% and shuts off automatically and then charge it to 100% without interruptions and repeat this cycle 2-3 times and the internal battery management system will calibrate the 0% and 100% to the respective battery terminal voltage.

This is true for mobiles and probably same works for car. So take my advice with some salt.

[Indian2003]

Originally Posted by srini1785

In our mobiles, there is a battery management system and time to time you need to calibrate your battery management system.

Interesting. My iPhone 11 Pro showed a battery health of 87% when the phone was only 1 1/2 years old and I was told that it was normal but the shop sent it in to Apple anyway.

It turned out to be the system files were corrupted. They asked me to do a fresh install and not from the backup in the cloud. When I did that the battery health went back up to 100%.

Could it be the same with cars?

[Shresth_EV]

Just searched a little on Google, you’re not alone. Few other owners are also facing this SoC drop issue.

PlugInIndia Nexon Thread

Looks like some of it gets mended itself during charging process in next cycle (one gentleman says that it jumped 8% during charging) after the SoC drop occurs and you put vehicle to charge. Could be the cell balancing like others note.

Some part of the said SoC drop is undoubtedly from vampire drain of electronics, just like all batteries lose some charge even when idle — so that’s that. If it’s double digit, it’s probably the cell balancing.

It’s also been noted that software had to be downgraded for owners. I suggest you check the link to that thread out. NexonEV Owners club also responded same to some users who took to Twitter for the issue.

Seems cell balancing/OS issue.

[DarthVeda]

it is just calibration gone wrong, that much % of charge can't disappear somewhere, laws of physics have to be obeyed.

[josephraj]

Well, it looks like some issue with the BMS. In the next charge cycle it jumped from 67% to 95% in about 30mins (slow charging at home!

The BMS is fairly complex, if one of the cell drops voltage then it will show that percentage.

So, it is either of two cases
1) One or more cells becoming weak (highly unlikely since it is a new car)
2) The BMS software has a bug (this is more likely now that I know others are facing the issue after the update)

The warranty on battery is 8 years. That is a bit of a relief but it looks like a lot of owners facing this issue and Tata is still firefighting :-(

[srini1785]

Originally Posted by Indian2003

Could it be the same with cars?

Not sure about iOS but in android, loss of battery calibration is a pretty common problem. There are continuous OS updates and these result in inducing a bug that affects the BMS. At least, that's the theory that i have.

As regards cars, OP's below message make it pretty clear.

Originally Posted by josephraj

Well, it looks like some issue with the BMS. In the next charge cycle it jumped from 67% to 95% in about 30mins (slow charging at home!

The BMS is fairly complex, if one of the cell drops voltage then it will show that percentage.

So, it is either of two cases
1) One or more cells becoming weak (highly unlikely since it is a new car)
2) The BMS software has a bug (this is more likely now that I know others are facing the issue after the update)

The warranty on battery is 8 years. That is a bit of a relief but it looks like a lot of owners facing this issue and Tata is still firefighting :-(

[abhishek46]

Originally Posted by srini1785

I am not a EV battery expert but here goes my 2paise.

In our mobiles, there is a battery management system and time to time you need to calibrate your battery management system. By that I mean that you have to let your mobile drain all of the battery till it is 0% and shuts off automatically and then charge it to 100% without interruptions.

As per my knowledge, we should never allow any battery (particularly Lithium based ones) to reach 0% charge.

We can take the example of the Lithium battery in the XL6/Ciaz.
It is clearly mentioned in the User manual of these cars, that 0% charge will result in the death of the battery.

From Team Bhp XL6 Review:

• Thanks to BHPian Leoshashi for sharing the price of the lithium-ion battery. It costs a whopping Rs. 53,685 to replace. Further, one must never let this battery discharge completely as it will not recharge again. Maruti recommends a minimum of 30 minutes of engine running time per week to prevent this from happening.

[srini1785]

Originally Posted by abhishek46

As per my knowledge, we should never allow any battery (particularly Lithium based ones) to reach 0% charge.

Any specific technical reason for this statement?. I am a bit surprised that batteries will not recharge (Li or not) after complete drain. Some long dead batteries tend to accumulate conductive particles in the electrolyte which cause shorting of electrodes but frankly did not understand why we need to keep 30mins of drive time left in a EV. Software reboot problems?.

[abhishek46]

Originally Posted by srini1785

Any specific technical reason for this statement?. I am a bit surprised that batteries will not recharge (Li or not) after complete drain. Some long dead batteries tend to accumulate conductive particles in the electrolyte which cause shorting of electrodes but frankly did not understand why we need to keep 30mins of drive time left in a EV. Software reboot problems?.

I am not very sure of the technical aspects.

However, if Maruti Suzuki (& other EV manufacturers) recommend against deep discharging on Li-Ion batteries, there may be some genuine reason behind it.

[josephraj]

The BMS should handle it. 0% does not mean 0volts. For e.g., if its a 4.2v cell, bms should cut at 3.5. The cells can be safely charged again. If bms allows for complete drain, that'spoor design

[srini1785]

Originally Posted by abhishek46

I am not very sure of the technical aspects.

I guess I have to withdraw my original statement as it appears to be false:

https://www.techrepublic.com/blog/fi...-battery-life/

See point 4

" 4: Avoid completely discharging lithium-ion batteries
If a lithium-ion battery is discharged below 2.5 volts per cell, a safety circuit built into the battery opens and the battery appears to be dead. The original charger will be of no use. Only battery analyzers with the boost function have a chance of recharging the battery.

Also, for safety reasons, do not recharge deeply discharged lithium-ion batteries if they have been stored in that condition for several months."

PS : Sometimes hedging statements like :

Originally Posted by srini1785

I am not a EV battery expert but here goes my 2paise.

Really saves you

[Shresth_EV]

Originally Posted by srini1785

why we need to keep 30mins of drive time left in a EV.

One doesn’t actually have to care about it manually, ie to remember to avoid using all the battery capacity down to 0%.

All EVs have locked buffer capacities, which means that even when your dash MID shows 0% or 1% critical charge left, you actually have more than that, which is exactly there to prevent deep discharge situations.

This buffer varies from company to company and vehicle to vehicle. You can even continue driving on the buffer capacity, but it’s strictly advised against it.



As per a one source I can’t seem to find it at the moment (I don’t remember where I saw it, but I think it was in a YT ownership video), the Nexon EV has effective capacity of 28600Wh or 28.6kWh, amounting to 1.6kWh in buffer. Which is actually worth 10-15km of range.



The MID will actually show you the range based on 28.6kWh capacity, ie after removing buffer from calculation algorithm.

Reasons behind avoiding deep discharge appear to be related to dissolution of anode material into electrolyte at low voltage, as per this citation on Wikipedia :

[Gaur]

Originally Posted by srini1785

I am not a EV battery expert but here goes my 2paise.

In our mobiles, there is a battery management system and time to time you need to calibrate your battery management system. By that I mean that you have to let your mobile drain all of the battery till it is 0% and shuts off automatically and then charge it to 100% without interruptions and repeat this cycle 2-3 times and the internal battery management system will calibrate the 0% and 100% to the respective battery terminal voltage.

This is true for mobiles and probably same works for car. So take my advice with some salt.

Lithium Ion batteries are strongly not recommended to be be completely discharged.

Most probably a bug in the BMS or some of the battery cells having issues.