[electric_eel]

The turtle mode gets activated in Tata EVs when the SoC drops below 10%. Here are some reasons not to drop the car below 10 % SoC.

1. The speed is capped at 55 Kmph. On highways if you are not careful this is dangerous.

2. Even on country roads it would be difficult to negotiate hilly terrain.

3. While the SoC drop is quite predictable in the 10-100% region things get tricky once below 10%

Turtle mode should have been the "Reserve" mode

The <10% SoC is a region of doubt in the charging graph of LFP batteries. That the DTE estimate shows "Recharge immediately" instead of any number is a good enough indication. Ideally Tata should have skipped the low performance mode completely. In addition to DTE showing "Recharge", they should have pitched the 10% SoC as the 0% SoC and marked the region below 10% as Reserve (See the formula below for conversion). As far as I know none of the other EVs have this low performance mode (even the ones with LFP battery).

What about the advice "go below 10% once in a while" ?

Although the Nexon EV manual does not say this, we have Anand Kulkarni on record suggesting this. Also BYD Atto's manual suggests going below 10%. SO this is a sound technical advice. However here are some caveat

1. Do this only if you are very close to your home.

2. Do this only when you have nothing better to do. Not when you have to hurry to the office. Not when doing a road trip etc.

3. Is the BYD's 10% SoC the same as Nexon' s 10% SoC ?

Interpreting the Tata SoC figures

If the SoC shows x % on your Tata EV, I would recommend that you take it as (x - 10) * 100/90 % SoC. The 10% SoC recommendation then becomes 19% SoC for Tata EVs which is a much more reasonable suggestion if you ask me.

The ARAI range for Nexon 40KWh then becomes 407 Kms and that of Nexon 45 Kwh becomes 438 Kms which is much much closer to reality. Every percentage then gives you roughly 4 kms in the ARAI cycle. Not bad if you ask me. There is hope of achieving this without AC in real world.

[GTO]

I never let my petrol / diesel fuel tank go below the quarter-tank mark, and I sure as hell wouldn't let my EV go below 25%. Especially when it's not as easy as ICE cars to top up the battery when you are out.

Just requires a little extra planning. That's all.

[Shreyans_Jain]

Originally Posted by GTO

I never let my petrol / diesel fuel tank go below the quarter-tank mark, and I sure as hell wouldn't let my EV go below 25%. Especially when it's not as easy as ICE cars to top up the battery when you are out.

Just requires a little extra planning. That's all.

It comes naturally once you get used to your car and its discharge rate. For instance, I started my day today with my Nexon EV at 34% charge. I know I’ll easily get through the day and reach home with approx 10-12% charge remaining. I am not at all worried about the battery % getting into teens or even into single digits if we are talking about my daily local commute. In fact, it is a best practice to do so every once in a while. Car’s behaviour is very predictable in this regard. At the same time, it will be a planning failure on my part if battery drops below 20% on highway runs.

[GoBabyGo]

Hi, my thoughts are always that whenever I buy an EV, it should have minimum 300 km range 90% to 20% in the city and minimum 250km range of 80% to 20% on highway.

I think MG & BYD 50kWh battery pack can realistically give this much range and I am hopeful that Tata 55kWh will be able to achieve such range.

Hope by the end of March 2025, we will see more EVs with 50kWh LFP battery (or blade battery), under 20 lacs onroad, mid or top variant (where there is no road tax).

[sharathkamath04]

On a long trip, we end up going below 10% due to multiple reasons like sudden ascending route, unavailability of chargers on planned route making you drive further, the destination being just another 5-10km and SOC being 10%.


No hard rule says "DO NOT GO BELOW 10%" from Tata or BYD. If that was the case, they must have made it an unusable battery (10% is a big chunk to be left out).

I have gone up to 2% 4-5 times and saw an HV error alert twice which went away after restart. I go below 10% mostly when using my car in the city.

I guess it's best to take it below 10% in the city (controlled environment) to avoid any unseen errors when the need arises.

[Edmund]

Turning turtle means something completely different, however, true still that you wouldn't want your TATA EV to turn turtle!!

[shyampsunder]

This is a very tricky concept but I am glad the post title makes things clear.

For Tata EVs, will never recommend going below 10% and go through the turtle mode.

In the case of BYD and MG, things get a lot more interesting.

For BYD, the manual is clear that it's recommended to take the car below 10% once in a while.

In MG's case, the manual doesn't say anything about it but there is a benefit in doing so.

In the LFP battery cars of MG, the SoH calculation by default is a time based one. Everyday, it drops by 0.01 irrespective of whether the car has been used or not. That's because in LFP batteries, computing SoH is very hard and hence there is a time based counter which keeps decrementing SoH which in turn reduces your range as well. But all of this is software driven and is not connected to your actual battery health.

Turns out that there is a way to do an actual SoH measurement and it is typically triggered by taking the battery below 20% and charging all the way to 100% on AC.

My hypothesis on what is happening is the following:

The BMS keeps track of how much energy has been consumed from the battery from the time it was full. Suppose the SoH is 95% that means the battery is able to hold only 95% of it's original capacity. When you take the battery to a low SoC, it's able to see how much energy has been dispatched and how much energy is left in the battery (Voltage curve is linear here and hence it works).

If the energy dispatched + energy remaining > SoH * battery size value, the SoH is recomputed.

I have managed to bump up my SoH several times by doing this. I was able to track this through my OBD.

Before starting the charging session:



After finishing the charging session:


As you can see the SoH went up from 96.69% to 97.06%.

In summary, in non Tata EVs, I do think its good to take the car below 10% or 20% once in a while especially if your car has an LFP battery.

[UP!!!!]

Originally Posted by GTO

I never let my petrol / diesel fuel tank go below the quarter-tank mark, and I sure as hell wouldn't let my EV go below 25%. Especially when it's not as easy as ICE cars to top up the battery when you are out.

Just requires a little extra planning. That's all.

Once you know enough about your car's capacity, you'll not be concerned about the battery % if you know that you're within the reach of a charger.

I was also kind of a person who would always refill the ICE car with fuel as soon as it reaches quarter tank. But now after driving EV for 2 years, I can drive my EV comfortably until 1% of battery If I know the route and charger.

Obviously, staying in NL or Europe helps in this situation because of charging infrastructure and Tesla's supercharger network. However it shouldn't be much different if you're aware about nearby chargers and it's availability.

[electric_eel]

Originally Posted by GTO

I never let my petrol / diesel fuel tank go below the quarter-tank mark, and I sure as hell wouldn't let my EV go below 25%.

I too was the 25% guy when using my Zen petrol but as others have pointed out, it is
very much possible to become comfortable with range prediction, particularly on trips
that you take often like home-office-home trips. And for LFP batteries it is indeed good
to take it to low SoCs (provided you charge all the way up to 100%).

Originally Posted by Shreyans_Jain

In fact, it is a best practice to do so every once in a while

Originally Posted by sharathkamath04

On a long trip, we end up going below 10% due to multiple reasons like sudden ascending route, unavailability of chargers on planned route making you drive further, the destination being just another 5-10km and SOC being 10%

My routine charging is like 15-20% SoC all the way up to 100%. Going below 10% may also be done but should be done with care on a Tata EV. I am not convinced by the need for turtle mode. They should have done away with it and pegged the lower SoC appropriately.

Originally Posted by Edmund

Turning turtle means something completely different, however, true still that you wouldn't want your TATA EV to turn turtle!!

Yes that was a deliberately chosen title. The pun very much intended.

Originally Posted by shyampsunder

This is a very tricky concept but I am glad the post title makes things clear.

For Tata EVs, will never recommend going below 10% and go through the turtle mode.

Okey this is new to me. Is it the ZS EV that you are talking about ? It is interesting that they determine the SoH thus. May be that is the real reason for going below 10 %. It is clearly not for bottom balancing as for that we need to really take out the cells and take them all the way to zero. Now things start making sense.

[Raghuwire]

Originally Posted by Edmund

Turning turtle means something completely different, however, true still that you wouldn't want your TATA EV to turn turtle!!

In a lot of electric equipment/ stackers/handlers which we use in industry there is a turtle mode, which means the machine will run slow (kind of like super ECO mode). This has nothing to do with turning turtle. I have seen this in most electric equipment/vehicles.

[sharathkamath04]

Originally Posted by electric_eel

My routine charging is like 15-20% SoC all the way up to 100%. Going below 10% may also be done but should be done with care on a Tata EV. I am not convinced by the need for turtle mode. They should have done away with it and pegged the lower SoC appropriately.

It is nice to have a warning at 25% SOC and turtle mode at 10%. At 10%, my priority must be to find the next charging station and how to reach it. It almost gives the 3-4km range per % in turtle mode, which can not be achieved if I drive above 50kmph. I would love to see a "turtle" mode selector where I can use it as per my SOC and distance to cover.

If they remove this 10% from the overall battery size and call it a reserve, the Nexon will have a 36kw and 27kw battery pack, reducing the realistic range to ~270 & ~210. I would have not purchased the car if the range was below 300.

The HV errors we see in Tata EVs at lower SOC may be due to various reasons. "High Voltage Error" is a very generic term. Tata must share more details about the error and not put it all under ONE generic error case.

[400notout]

With my Nexon Ev, I follow a very simple thumb rule. Its time to recharge when the sports mode gets deactivated i.e. 25 %. My daily commute is 60kms which takes out between 15 to 20 percent of the battery. At 25% I can get max 40 to 45 kms before it's gets below 10%. Also if you get stuck in an extraordinary traffic jam you might end up using twice the amount on a single trip. Once the range showed 120 kms while leaving for office but due to a massively slow traffic movement I reached my destination an hour late and by the time I reached office it showed 70kms. Now I could experiment taking it back home, but I'd rather not push my luck with a TATA ev. So I went to the mall near my office and charged it there. Till now the lowest I've gone is 16% and I do not wish to experiment further.

For outstation trips the farthest I've been is to Pune from Thane. When I reached it showed a range of 130 kms. I charged at my relatives 15 amp socket overnight and drove comfortably back home. For people with lower trip averages and availability of chargers at both destinations it might be worthwhile to experiment. But in my use case it's a strict no-no, so I regularly recharge when 20 to 25% charge is left.

[TwinBishop]

Discharging a lithium battery below even 20% is generally not advisable. The greater the discharge the more will be the increase in battery temperature while recharging. And, lithium batteries are sensitive to temperature. The long term battery life may reduce.

Of course modern BMS in EVs might be managing all this. But the basic limitations of lithium ion chemistry with regard to temperature remain. This concern is even more valid in a tropical country like ours.

[electric_eel]

Originally Posted by TwinBishop

Discharging a lithium battery below even 20% is generally not advisable. The greater the discharge the more will be the increase in battery temperature while recharging. And, lithium batteries are sensitive to temperature. The long term battery life may reduce.

Of course modern BMS in EVs might be managing all this. But the basic limitations of lithium ion chemistry with regard to temperature remain. This concern is even more valid in a tropical country like ours.

What you said is correct for both NMC and LFP batteries cells. However for battery packs, particularly LFP based, this optimisation of life time should be traded off with the ability to better predict SoC and as a consequence the range and DTE. The battery pack of a typical EV will easily outlast the car, however if we do not do proper charging, the lack of battery balancing will lead to innumerable usability issues. Think about it, if we cannot trust the SoC shown on our display what use is the saved battery life.

May be I should have toned down a bit more. In decreasing order of priority, with the last having very little priority ensure that.

1. When charging at home (slow charging) always (try to) charge till 100%

2. Bring the battery to as low as 15-20 % before charging.

3. It is desirable to bring the battery to <10% SoC once in a while but this should be very carefully. Do this step only if you are sure you can manage it.


Charging till 100% is a must for battery balancing and is very important for LFP based packs. Whenever possible one should not get too worked up if we miss it once or twice. After all whenever we use regen we do recharge batteries often at high power with no consideration on balancing.

[TwinBishop]

Originally Posted by electric_eel

The battery pack of a typical EV will easily outlast the car, however if we do not do proper charging, the lack of battery balancing will lead to innumerable usability issues.

1. When charging at home (slow charging) always (try to) charge till 100%

2. Bring the battery to as low as 15-20 % before charging.

3. It is desirable to bring the battery to <10% SoC once in a while but this should be very carefully. Do this step only if you are sure you can manage it.

Thanks for the detailed explanation. Agree with all the points. Manufacturers do recommend that you need to discharge below 10% occasionally and recharge to 100% so that the battery charge meter is recalibrated and SoC is measured accurately.