About this replacement
TomTom One V4 Series — 3.7V Li-ion Replacement Battery (AHL03709900)
This is a 3.7V, 900mAh Li-ion cell built to the AHL03709900 specification. It fits the TomTom One V4, One V4 Traffic, One V4 Classic, and One V4 Assist portable GPS navigators. Voltage and capacity match the original factory cell exactly.
- One V4 platform compatibility: The V4 Traffic, Classic, and Assist variants all share the same battery bay dimensions and 3.7V power rail. The connector and BMS handshake are identical across these models, so one cell covers the full range.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the One V4 platform. The BMS accepted the cell without fault codes, and the unit powered on and held charge through repeated navigation sessions.
- First-fix cold start after swap: After fitting this cell, power the GPS on outdoors and let it acquire a satellite fix before driving. A full power interruption triggers a cold start — first fix takes 5–10 minutes. Subsequent warm starts drop to under a minute once the almanac data rebuilds.
GPS accuracy reduced at low battery on the One V4
The One V4 scales back GPS receiver sensitivity as cell voltage drops toward the low-voltage cutoff. This is a firmware-level power-saving behaviour, not a hardware fault. Position accuracy degrades and the unit may struggle to maintain a fix in areas with moderate signal. Keeping the cell above 3.5V during active navigation prevents the sensitivity reduction from triggering.
One V4 shuts off without warning before the battery indicator reaches empty
The voltage-threshold calibration in the One V4 firmware is tuned for the original cell's discharge curve. A new cell may discharge at a slightly different rate, causing the unit to hit its hardware cutoff voltage before the on-screen indicator reaches the final bar. The device reads the indicator off a lookup table, not a live fuel gauge. To recalibrate, run two full charge-to-cutoff cycles — the indicator tracks more accurately once the firmware has sampled the actual discharge curve of the new cell.