Logitech K800 Wireless Keyboard Replacement Battery 3.7V 1500mAh

Logitech K800 — 3.7V Li-Polymer Replacement Battery (802085P)

This 3.7V, 1500mAh Li-Polymer battery replaces the internal cell in the Logitech K800 wireless illuminated keyboard. It fits the K800 directly using OEM part number 802085P. If your K800 is no longer holding a charge or losing power faster than it used to, this battery addresses that directly.

• K800 keyboard platform: The K800 uses an internal Li-Polymer cell rather than user-swappable AA or AAA cells. The backlight draws continuous current on top of the wireless radio load, which degrades the original cell faster than a non-illuminated keyboard would experience.
• Bench tested on actual hardware: We cycled this battery through the K800's BMS and confirmed stable handshake at full charge. The BMS accepted the cell without fault flags, and charge termination triggered cleanly at 4.2V.
• Backlight draw management: The K800 adjusts backlight brightness automatically based on ambient light. Running maximum brightness continuously accelerates cell depletion — set the backlight to proximity-only activation mode in Logitech Options software to reduce the constant current draw on the new cell.

K800 pairing lost after battery replacement

When the K800's internal battery fully depletes, the keyboard's memory of its Unifying receiver pairing can drop. This happens because the Unifying pairing data is held in a section of the keyboard's firmware that depends on a minimum voltage to retain state. After fitting the new battery, unplug the Unifying receiver, wait ten seconds, then replug it. If the keyboard still does not respond, use Logitech's Unifying software to re-pair — this takes under two minutes and restores full function.

K800 showing full charge indicator but cutting out during use

This symptom points to a degraded original cell, not a charging circuit fault. A worn Li-Polymer cell can report a near-full state of charge at rest but collapse under the combined load of the wireless radio and backlight. The voltage sags below the BMS cutoff threshold under load even though the resting voltage looks acceptable. Fitting a fresh cell at full rated capacity — 1500mAh — eliminates the voltage sag and the unexpected cutouts that follow it.