About this replacement
Mitac Mio A500 / A501 / A502 — 3.7V Li-ion Replacement Battery (EM3T171103C12)
This 3.7V 1200mAh Li-ion cell replaces the original battery in the Mitac Mio A500, A501, and A502 portable GPS navigation devices. These mid-2000s touchscreen units lose charging capacity over time as the original cell degrades. Swapping this cell restores normal power behaviour to the GPS hardware.
- Mio A500 / A501 / A502 compatibility: All three Mio models share the same battery bay dimensions, connector pinout, and 3.7V supply rail. The BMS handshake protocol is identical across the A500 series, so one cell fits all three without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Mio platform. The BMS accepted the cell without fault flags, held stable voltage through GPS acquisition, and cut off cleanly at the low-voltage threshold without triggering a hard reset.
- Fuel gauge recalibration on first cycle: After fitting this cell, run one complete discharge down to auto-shutoff before recharging. The Mio's fuel gauge IC was calibrated against the original cell curve — a full cycle gives it a new reference point, so the percentage readout tracks accurately from the second charge onward.
Why the Mio A500 shows wrong battery percentage after a cell swap
The Mio A500 uses a coulomb counter IC that builds its capacity model from accumulated charge and discharge data on the original cell. When a new cell goes in, the IC still references the old discharge curve. This causes the percentage display to jump, stall, or read high until the IC observes a full discharge-to-cutoff cycle on the new cell. After one complete cycle, the counter resets its reference and tracks correctly. No hardware fix is needed — the recalibration happens automatically after that first full discharge.
Sudden shutdown while the GPS is actively routing
This happens when the cell voltage drops below the GPS chipset's minimum operating threshold under load — typically around 3.2V — even if the percentage display still shows charge remaining. GPS acquisition and screen backlight together pull more current than idle state, exposing voltage sag in a cell that reads fine at rest. If the device shuts off mid-route and restarts normally on charge, the cell is hitting that sag threshold. Check that the replacement cell is seated flush and the connector contacts are fully engaged — a loose contact raises internal resistance and accelerates sag.