About this replacement
TomTom ONE IQ / V5 — 3.7V Li-ion Replacement Battery (6027A0089521)
This 3.7V, 900mAh lithium-ion cell replaces part number 6027A0089521 in the TomTom ONE IQ and V5 portable GPS navigators. It fits models including 4EK0.001.01 and restores power to units where the original cell no longer holds a charge. Dimensions are 45.20 × 34.24 × 5.70mm — measure your existing cell before fitting if you are unsure.
- ONE IQ and V5 platform fit: These models share the same PCB connector pinout and 3.7V single-cell architecture. The BMS on both units monitors cell voltage at the same cutoff threshold, so this cell communicates correctly with the protection circuit on either device.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the ONE IQ platform. The BMS accepted the cell without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff — no forced shutdowns during the charge phase.
- First power-on after fitting: After fitting this cell, take the unit outdoors and power it on before driving. The GPS performs a cold start after any full power interruption — first satellite acquisition takes 5–10 minutes. Subsequent warm starts drop to under a minute once almanac data is cached.
GPS accuracy reduced at low battery on the ONE IQ
The TomTom ONE IQ GPS receiver pulls consistent power to maintain signal sensitivity. At low cell voltage — typically below 3.5V — some units reduce receiver gain to protect the remaining charge, which can cause position drift or signal loss mid-route. The fix is straightforward: keep the cell above half charge on long trips. If you are seeing degraded accuracy only near the end of a charge cycle, the receiver is throttling — not the antenna or software.
Device shuts off without warning before the battery indicator reads empty
After a full battery swap, the charge indicator on the ONE IQ is uncalibrated against the new cell's discharge curve. The unit can show two bars on the icon and cut off seconds later. This happens because the device's voltage-to-percentage map was built around the original cell's aged characteristics. Charge the replacement cell to 100%, run it through two full discharge cycles under active navigation, and the indicator will re-anchor to the new cell's actual cutoff — around 3.2V.