About this replacement
Xiaomi 70mai Pro / A500S — 3.7V Li-ion Replacement Battery (HMC1450)
This is a 3.7V, 900mAh Li-ion cell that replaces the internal battery in the Xiaomi 70mai Pro and 70mai A500S dashcams. It fits the Midrive D02 and Midrive D04 as well — all share the same HMC1450 cell and internal connector layout. This battery powers the camera's parking mode recording when the vehicle ignition is off and no hardwire power is present.
- 70mai Pro / A500S / Midrive D02 / D04 compatibility: These models share the same compact internal cell format, voltage rail, and protection circuit interface. The HMC1450 cell fits all four without modification to connectors or mounting.
- Bench tested on actual hardware: We cycled this cell through the 70mai Pro's internal BMS handshake and confirmed the protection circuit trips correctly at low-voltage cutoff. Charge acceptance and cutoff voltage both tracked within spec across multiple cycles.
- First-cycle parking mode calibration: After installing a new cell, complete one full drive with the camera powered via USB or hardwire before relying on parking mode. The dashcam's power management logic needs a full charge-discharge reference cycle to accurately gauge available parking mode capacity from the new cell.
Why the 70mai Pro drops out of parking mode before expected
The 70mai Pro uses its internal battery exclusively for parking mode — it draws from this cell continuously while monitoring for motion or impact events. A degraded cell with reduced capacity will hit the low-voltage cutoff sooner than the camera's firmware estimates, cutting parking mode short. The camera's displayed parking mode duration is calibrated against cell voltage curves that assume a full 900mAh cell. Replacing the cell restores the voltage profile the firmware expects and extends recording duration back to normal.
Footage files corrupt or missing after parking mode session
If the internal cell voltage sags mid-write, the dashcam loses power before it can finalise the active video file. The file system closes abruptly, leaving the last clip unreadable or absent from the SD card. This is most common in hot weather — an enclosed dashboard environment raises cell temperature, which accelerates voltage sag under sustained recording draw. Replace the cell and check that the SD card is formatted correctly inside the camera, not via a PC, to ensure clean file allocation from the first write cycle.