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Live Sayuk EVDS, EV battery diagnostics

Know the battery before you close the deal.

Plug an OBD adapter into an EV and see what its battery management system actually reports: health, the weakest cell, temperatures, and how they move over months. Every figure says where it came from.

Download the trade brochure Get the Android app Open it in a browser
  • UN GTR 22Health graded against the published floor
  • Read-onlyAsks the car questions, never changes it
  • Free todayAndroid and web, iPhone through Bluefy
Tata Punch.ev 102 cells · LFP
State of charge
56.4%
Measured
Cell spread
5mV
Measured
Sigma
0.99mV
Derived
Efficiency
7.1km/kWh
Modelled

Lowest cell #51 in 21% of scans, against 1% by chance.

11,600+ scans recorded, 12 to 29 Sep 2026
241,000 time-series samples behind them
29 EV configurations with a built profile
11 of them scanned on real cars

Most battery apps tell you a number. This one tells you whether to believe it.

An OBD tool can show a per-cell voltage grid for a car that publishes no per-cell voltages. It can print a firmware date it never read. It can call an insulation reading "safe" when the vehicle reported nothing at all. Nobody notices, because the screen looks better with those than without.

Measured

Read straight from an ECU: state of charge, pack voltage and current, the highest and lowest cell and which ones they are, temperatures, odometer.

Derived

Arithmetic on measured values, nothing assumed. Pack power is voltage times current. Cell spread is highest minus lowest.

Modelled

Needs an assumption the car does not report: energy in kWh, efficiency, the per-cell grid. Useful on screen, and never printed as a measurement.

Same healthy pack, two very different readings

At 100% charge every LFP pack shows a wide cell spread, often 150 to 260 mV. At 95 to 97% the same packs read 4 to 10 mV. Judging at the wrong charge fails good cars, so EVDS reads spread only from 95 to 99%.

2501000 0%50%100%mV Too flat to judge Read here 4–10 mV 150–260 mV at 100% Schematic of a typical healthy LFP pack.

One document the whole deal can rely on.

The Battery Health Report is built from the car's own scans. Every figure can be traced to a reading the adapter took, and anything the car did not answer says so.

  1. A grade with a confidence line Built from up to four components. A component the car could not produce is left out, and the report says so.
  2. Health against the floor for this car's kilometres Not a generic pass mark. 92% at 1,40,000 km is excellent. 92% at 18,000 km is not.
  3. Spread read where it means something Only between 95 and 99% charge. Below that an LFP pack is too flat to judge.
  4. Findings are sentences with evidence The claim, the numbers behind it and, only when useful, what to do. If nothing fires, nothing is printed.
  5. The identity a dealer checks Firmware versions and flash dates from the car. Unanswered fields read "Not read", never a stand-in.
Read all 11 pages in the brochure

Built for the people who buy, sell and service EVs.

Used-EV resellers

Price the battery, not the badge.

Read the pack at intake, before you quote. Attach the Battery Health Report to the listing as a PDF or a link, and scan again before handover to see whether anything moved.

  • State of health vs GTR 22
  • Cell extremes
  • Odometer from the car
  • Shareable report
  • Compare two sessions

EV service centres

See what the car saw, then show the owner.

Live numbers, the history behind them and a document to hand over. When the car says "battery warning" and the scanner says nothing, this is the evidence in between.

  • Weakest-cell tracking
  • Seven powertrain temperatures
  • Fault codes in plain language
  • Controller identity
  • 12V and insulation

What one scan can and cannot do. A first scan gives measured readings, findings and the controller's identity. The letter grade needs evidence from charge sessions, so a car scanned once shows "More readings needed" with a checklist of what is missing. For the strongest report, connect during a slow AC charge through 95 to 99%. The app guides the capture.

What it does

Finds the cell that keeps failing

A pack stops when its weakest cell stops, not when the average does. Across a car's history the app tracks which cell is lowest each time. On a 102-cell pack any cell is lowest about 1% of the time by chance, so one appearing in a fifth of the scans is telling you something.

Knows when a reading cannot mean what it seems

On LFP a cell's voltage barely moves between 20% and 80% charge, about 0.7 mV per percent, against a controller reporting whole millivolts. EVDS will not call a mid-charge spread an imbalance, because at that charge it cannot be one.

Reads seven powertrain temperatures

Motor winding, inverter, AC compressor, both PDU busbars, DC-DC converter and inverter coolant. Each tile shows how old its reading is, and a sensor that stops answering disappears rather than freezing on a stale value.

Logs the session by itself

Connect the adapter and recording starts. No button to press and none to forget. Readings are stored on the phone and upload when there is a connection.

Keeps a history that means something

Trends are computed per car. Cell 69 on another car is a different cell, and pooling two vehicles makes a chart that looks meaningful and is not.

Exports a report you can hand over

A PDF with the pack's measured state and the controller firmware and flash dates read from the car. Modelled values are excluded by design.

29 configurations across six brands.

Tata has the deepest coverage, proven on real cars every day. Other brands have profiles built and ready. A few newer models still read only part of the pack. Each profile carries the pack's chemistry, cell count and layout, so a 102-cell Punch and a 118-cell Harrier are read on their own terms.

Tata

  • Punch EV25, 35, 40 kWh (two packs)
  • Nexon EVPrime, Max, 45 kWh
  • Tiago and Tigor EV19.2 to 26 kWh
  • Curvv EV45, 55 kWh
  • Harrier EV65, 75 kWh
  • Sierra EV75 kWh

MG

  • Windsor EVPro, 52.9 kWh
  • ZS EV50.3 kWh
  • Comet EV17.3 kWh

BYD

  • Atto 3, Seal60.5, 82.6 kWh
  • Dolphin, Dolphin Mini44.9, 38 kWh

Mahindra

  • XUV400 EV39.4 kWh
  • XUV 3XO EV39.4 kWh
  • BE 6, XEV 9e, XEV 9S79 kWh

Hyundai and Kia

  • Hyundai Ioniq 572.6 kWh
  • Kia EV6GT-Line, 77.4 kWh
Scanned on real cars Profile ready Partial readings for now

With the owner's consent, EVDS also compares a car with others of the same model in plain words, such as "healthier than 6 of the 9 Nexon EV Max cars counted". Nothing shows until at least 5 cars are counted.

Your data, on your dashboard, in your software.

Built to order

Every scan is already recorded per car, with its readings and findings. We build the views and connections your team needs on top of that. This is done per customer, it is not a self-serve feature yet.

Intake boardExample dashboard, illustrative figures
148cars scanned this week
91%median state of health
9flagged for review
23waiting for a top-of-charge scan
RegistrationModelHealthSpread at 95–99%Decision
TS09 ··· 4127 Nexon EV Max 93% 8 mV Cleared
KA05 ··· 8830 Punch EV 35 88% 14 mV Watch
MH12 ··· 2094 Tiago EV 90% n/a Re-scan
AP28 ··· 6512 Harrier.ev 75 96% 6 mV Cleared
Sayuk EVDSScans, readings, findings, reports
Your systems Listing platform, dealer or workshop software, CRM and job cards, warranty and claims, BI and reporting
  • REST API
  • Webhooks
  • Scheduled export
  • Database sync

Dashboards for each role

One view per role: inspector, branch, head office, insurer.

Rules and alerts

Flag a car when health, spread or a repeat weak cell crosses your own threshold.

Your branding

The same measured report, carrying your name, colours and wording.

Workflow hooks

Attach the report to the listing, open the job card, notify the buyer, automatically.

  1. 1 Tell us the workflow Who scans, who decides, which systems hold the truth today.
  2. 2 We map the fields Your car and customer records matched to EVDS scans.
  3. 3 Pilot on your cars A dashboard and a sync, tried on real vehicles from your lot or bay.
  4. 4 Go live, then refine Rules and views adjusted as your team uses them.

It reads. It never writes.

You are plugging into someone's car. EVDS only asks the controller for readings. The rule is an allow-list, checked on the phone that owns the adapter, so anything not listed is refused by default, including services added to the diagnostic standard tomorrow.

Allowed: questions the car answers

  • ReadData by identifier, such as health and cell voltages
  • ReadCurrent data, freeze frames and vehicle information
  • ReadStored and pending trouble codes
  • OpenA diagnostic session, and keep it alive

Refused: anything that changes the car

  • WriteData to controller memory
  • RunManufacturer routines and actuator tests
  • Reset, clearControllers, fault history, adaptation data
  • SilenceBus messages, or switch off fault detection

Try it without an account. Download everything you have recorded, or ask for deletion, which can be undone for 30 days. Diagnostic codes and raw readings are never shown to other members, and peer comparison is opt-in and anonymous.

Getting it

Android

The full app, installed on the phone. Works with no signal, connects to Bluetooth adapters natively, and is the only way to use a Wi-Fi OBD adapter, which speaks a protocol no browser is permitted to open.

Download the APK

iPhone and iPad

Safari does not implement Web Bluetooth, and every iOS browser is Safari underneath, so no iPhone browser can reach an OBD adapter. The workaround is Bluefy, a free browser on the App Store that adds it: install Bluefy, open evds.sayuk.cloud inside it, and connect as normal.

A native iOS build is not available yet.

A diagnostic aid, not a verdict. It reads what your car publishes and is careful about what it claims from it. A reading that worries you is a reason to talk to a qualified service centre, with the exported report in hand.

Bring a car. We'll bring the report.

Tell us how you buy, sell or service EVs, and we will show you what the battery says on a car from your own lot or bay. You need an Android phone and an ELM327-type Bluetooth or Wi-Fi OBD adapter.

hello@sayuk.cloud Trade brochure (PDF) Open the web app