OBD dongles and apps like LeafSpy are useful tools — but they have a fundamental limitation most buyers do not know about. Here is an honest comparison of what each tool actually measures, where OBD falls short, and when you need an independent certified test.
When you plug in an OBD dongle and open LeafSpy Pro, you are reading the Battery Management System (BMS) data feed. The BMS monitors the battery and reports what it thinks is happening. The problem: the BMS is not an independent auditor of its own battery.
The BMS can compensate for weak cells by limiting their use. SOH still reads reasonably well — but the underlying cell condition is worse than the number suggests. Aviloo has found hidden cell damage in batteries showing 89% SOH on the BMS readout.
The BMS SOH calculation can drift from reality over time, particularly on Nissan Leafs. A software recalibration can change the displayed SOH without changing the actual battery condition.
| Feature | LeafSpy / OBD | Aviloo (PAD) |
|---|---|---|
| Data source | BMS self-report | Independent cell-level test |
| Works on all EVs? | Nissan Leaf only (LeafSpy) | 500+ EV and PHEV models |
| Detects hidden cell faults? | No | Yes — Red Flag alerts |
| Third-party certified? | No | Yes — TUV certified |
| Certificate issued? | No — screenshot only | Yes — official Aviloo PDF |
| Best use case | Monitoring your own Leaf | Buying, selling, warranty |
| Cost | Free / £10-30 dongle | £79 — PAD South Wales |
PAD is South Wales only Aviloo-certified mobile EV battery testing service. Independent cell-level analysis. Official TUV-certified certificate. Mobile — we come to you.
