About this replacement
Magellan Maestro 4200 / 4250 Series — 3.7V Li-ion Replacement Battery (K4790SA108821)
This 3.7V 2200mAh Li-ion cell replaces the original battery in the Magellan Maestro 4200, 4210, 4220, and 4250 portable GPS navigators. All four models share the same battery bay dimensions (70.10 × 50.41 × 5.50mm) and use the OEM part number K4790SA108821. Fit this cell when the original no longer holds a charge or the unit shuts off unexpectedly during navigation.
- Maestro 4200 / 4210 / 4220 / 4250 fitment: These four units share an identical battery bay, connector pinout, and charge management circuit. One cell covers all four — no adapter or wiring change needed.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Maestro platform and confirmed the BMS accepted the cell without fault codes, held the 3.7V nominal rail cleanly, and terminated charge correctly at 4.2V.
- Cold-start satellite acquisition after power swap: After fitting this cell, power the unit fully on outdoors before your first drive. The GPS performs a cold start after any full power interruption — first satellite fix takes 5–10 minutes in open sky versus under a minute for subsequent warm starts.
GPS accuracy dropping as the Maestro 4200 battery runs low
At low state of charge, the Maestro's power management pulls back receiver sensitivity to keep the CPU and display running. This reduces the number of satellites the unit can track, which widens the position error circle. You may notice routes recalculating more often or the position dot jumping between lanes. Keeping the cell above 3.5V under load avoids this threshold.
Maestro 4200 shutting off without any low-battery warning
The on-screen battery indicator on the Maestro 4200 reads from a fuel gauge that was calibrated to the original cell's discharge curve. After a battery swap, that calibration is off — the indicator can still show two bars when the cell is already near cutoff voltage. The BMS then trips the protection circuit and the unit cuts power with no visual warning. Run two full charge-to-shutdown cycles to let the gauge recalibrate, and expect accurate readings from the third cycle onward. If the unit cuts off abruptly, charge it back to 4.2V and repeat the cycle.