About this replacement
Logitech MX KEYS / YR0073 — 3.7V Li-Polymer Replacement Battery (533-000177)
This 3.7V, 1500mAh Li-Polymer cell replaces OEM part 533-000177 in the Logitech MX KEYS wireless keyboard and YR0073 variants. It restores power to both the wireless connectivity and the backlit keys. Capacity figures are taken directly from product data — 5.55Wh total.
- MX KEYS and YR0073 fitment: Both models share the same 3.7V single-cell Li-Polymer architecture, the same connector pinout, and the same BMS handshake profile — so one cell covers both boards without any modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an MX KEYS board. The BMS accepted charge at the standard rate, backlight control remained active throughout, and the Bluetooth module held its pairing without reset.
- Backlight draw management: The MX KEYS dims or disables backlighting automatically as voltage drops toward the low-cutoff threshold. If you notice backlight flicker or sudden dimming before the keyboard shows a low-battery alert, the cell is likely near end of life — not a firmware fault.
Keyboard pairing lost after battery swap on the MX KEYS
When the MX KEYS loses power completely during a battery swap, the onboard BMS resets and the keyboard can drop its Bluetooth or Logi Bolt pairing. This happens because the pairing state is held in volatile memory that needs a stable voltage rail to persist. To recover, hold the Easy-Switch button for the relevant channel until the LED blinks fast, then re-pair from your device's Bluetooth settings or re-plug the Logi Bolt receiver. Target a stable 3.7V from the new cell before pairing to avoid a second drop-out.
Backlight turns off and keyboard stops responding before battery indicator hits zero
The MX KEYS firmware applies a conservative low-voltage cutoff — typically around 3.0V — to protect the Li-Polymer cell from deep discharge. If the cell has aged and its internal resistance has risen, voltage sags under the combined load of wireless polling and backlighting faster than the reported percentage suggests. The keyboard cuts both loads simultaneously to avoid damaging the cell further. Replace the battery when you see this pattern; capacity reporting will not improve with charge cycles on a degraded cell.