A Tale of Two Xs: Why a "Parked" EV Scan Isn't Enough
By: Joel Davis, Founder and Lead HV Specialist, Elektrowagen Consulting LLC
THE BOTTOM LINE (TL;DR): A stationary EV scan only tells you how the battery looks while parked. To see if a battery is actually dying from high internal resistance, you have to test it under a heavy dynamic load. Below is the hard telemetry data from two Model Xs that proves why you should never buy a used EV based on a basic “Health Score.”
If you are shopping for a used EV, the most common advice you will hear is to plug a basic scanner into the car or check the dashboard range before you buy. If the screen says the battery is at 80% or 90% health, you are good to go, right?
Not necessarily.
As a High-Voltage Specialist, I see the limits of basic testing every single day out in the field. I want to show you exactly why a static “parked” scan is just the tip of the iceberg, and why you need to put a battery under a heavy dynamic load to see the truth.
To prove it, let’s look at the hard data from two different Tesla Model Xs my mobile unit scanned recently.
The Setup: Mileage Does Not Equal Health
We are looking at two vehicles we recently diagnosed:
Vehicle 1: A 2016 Tesla Model X P90D with 72,912 miles on the odometer.
Vehicle 2: A 2018 Tesla Model X 100D with 98,239 miles on the odometer.
Despite the 2018 Model X having over 25,000 more miles on it, it drastically outperforms the 2016 model across every physical metric.
The Static Illusion
Before we drove the 2016 Model X, we performed a basic static (or “Blitz”) test while the car was parked. If you only looked at this stationary data, you would think this is a perfectly fine, slightly aging battery:
It registered a State of Health (SOH) of 81%.
It received an “A” rating for Static Voltage Consistency.
The maximum voltage delta (the difference between the highest and lowest battery “bricks”—which are clusters of individual cells) was a tiny 5 millivolts.
The battery system showed zero fault codes detected.
On paper, sitting in a parking lot, this battery looks safe and stable. But what happens when you actually ask it to do some heavy lifting?
The Dynamic Truth (The Stress Test)
To see a battery’s true health, you have to hit the accelerator and measure how the internal hardware reacts when pulling massive power. Here is exactly what the data showed when we pushed both vehicles during a dynamic load test.
1. The Voltage Floor (The Safety Net)
The most critical metric during a high-amperage launch is how far the voltage sags.
During its test, the 2016 P90D pulled a peak of -1318.80A.
Under this load, the total pack voltage plummeted to a dangerously low 249.75V.
Looking at the telemetry, Brick #26 collapsed down to 2.538V.
This is an incredibly weak floor, resting dangerously close to the 2.5V threshold where permanent physical damage and lithium plating occur.
The 2018 100D, on the other hand, pulled a similar heavy load of -1250.70A, but the total pack voltage maintained a robust 305.15V.
Its lowest point (Brick #3) only sagged to 3.143V.
The 100D pack easily absorbs the physical stress of a hard launch, whereas the P90D pack is gasping for breath and forcing the car’s computer to throttle power to prevent a catastrophic brick failure.
2. Internal Resistance (The “Clogged Artery”)
Internal resistance is the physical barrier that causes voltage sag and generates heat. As the lithium-ion cells inside these bricks age chemically, this resistance climbs. Think of it like trying to run a sprint while breathing through a drinking straw.
This 2016 P90D pack shows severe internal aging.
The internal resistance on Brick #26 is a massive 1.700 mΩ.
Across the board, dozens of bricks in this pack are operating with a resistance above 1.300 mΩ.
The 2018 100D is completely different; the internal resistance is incredibly tight and low. The highest resistance in the entire 2018 pack is Brick #45 at just 0.660 mΩ.
This means the P90D bricks are working more than twice as hard to push the exact same amount of electricity.
3. Thermal Management (The Heat Problem)
Because the 2016 P90D has such high internal resistance, that wasted energy converts directly into heat under load.
During the brief 5-minute dynamic test, the 2016 battery experienced massive thermal spikes. Sensor T28 recorded a severe 35.8°F fluctuation, reaching a peak of 88.3°F.
Benefitting from lower resistance and a superior pack architecture, the 2018 100D remained remarkably stable. The absolute maximum temperature fluctuation recorded across any sensor was only 5.4°F.
The $50 Dongle Confusion
I see this all the time: an owner plugs a $50 Bluetooth dongle into their dash, opens an app on their phone, and sees a screen full of battery voltages. To the untrained eye, it looks like granular, professional data.
But here is the catch: polling rate and BMS smoothing. Modern Battery Management Systems (BMS) are incredibly efficient at rapidly balancing voltage across the pack to keep the car running. A cheap dongle and a phone app communicate slowly, taking a snapshot of the battery maybe once every few seconds. Because the app’s polling rate is so slow, it completely misses the raw, real-time peaks and valleys of the hardware during a hard launch.
Instead of showing you the terrifying millisecond that Brick #26 collapsed to 2.538V, the app shows you a “BMS smoothed snapshot” that artificially hides the bad bricks. Our professional EV diagnostic computers poll the vehicle’s CAN bus at lightning speed, cutting through the BMS’s smoothing to capture the exact millisecond a brick gasps for air. You simply cannot get that depth of sampling from a consumer smartphone app.
The Tech Takeaway: Look Deeper
You cannot judge an EV battery by its mileage, and you certainly cannot rely on a parked, static scan or a cheap phone app. The 2016 Model X looked incredibly consistent when it was sitting perfectly still. But the moment we asked it to perform, the high internal resistance choked the pack, causing massive heat spikes and terrifying voltage collapses.
If you are buying a used EV or bringing a vehicle out of warranty, protect your wallet by demanding a dynamic, high-frequency load test to see how the high-voltage “engine” actually performs when you hit the gas.
Ready to Know the Truth About Your Battery?
At Elektrowagen Consulting LLC, we don’t guess your battery’s health from the cloud. We come to you and plug directly into the hardware.
If you are looking to purchase a used EV, or simply want to know the true mechanical health of your current vehicle, visit us at ElektrowagenConsulting.com to book a professional, direct-connect dynamic scan.