If the SoC shows x % on your Tata EV, I would recommend that you take it as (x – 10) * 100/90 % SoC.
BHPian electric_eel recently shared this with other enthusiasts:
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.
Here’s what GTO replied:
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.
Here’s what BHPian Shreyans_Jain replied:
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.
Here’s what BHPian shyampsunder replied:
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.
Check out BHPian comments for more insights and information.
