About this replacement
Logitech Harmony 1000 / 1100 Series — 3.7V Li-ion Replacement Battery (F12440056)
This 3.7V, 1300mAh Li-ion battery replaces the original rechargeable cell in the Logitech Harmony 1000, 1100, 1100i, and 915 remote controls. The original cell degrades with each charge cycle, eventually failing to hold enough charge to keep the remote responsive. Swapping this battery restores the remote to full operating condition.
- Harmony 1000, 1100, 1100i, and 915 compatibility: These remotes share the same internal battery bay geometry, connector pinout, and 3.7V power rail. One battery part number — F12440056 — covers the full family without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Harmony 1000 unit. The onboard charge controller accepted the battery immediately, and the BMS held a stable 3.7V nominal output across the full discharge curve with no cutoff trips under normal remote-control load.
- Connector seating on the Harmony 1000: The JST-style connector on this battery must click fully into the socket before closing the back panel. A half-seated connector causes an intermittent connection — the remote appears dead even with a fully charged cell. Press until you hear the latch engage.
Why the Harmony 1000 stops responding before the battery looks fully drained
The Harmony 1000 drives an IR LED array that requires a minimum voltage to fire at usable range. As a Li-ion cell ages, its internal resistance rises — voltage sags under the brief high-current pulse each IR burst needs, even if the resting voltage reads acceptable. The remote's display may still light up while the IR output has already dropped below the threshold your TV or receiver can detect. Replacing the battery eliminates that internal resistance problem entirely, because a fresh cell delivers the current spike without the voltage drop.
Harmony 1000 shows charging but remote still won't wake up
This symptom usually points to a deeply discharged original cell that has dropped below the BMS reinitialisation threshold — typically under 2.5V on a 3.7V Li-ion cell. The charge indicator activates because the dock is applying voltage, but the battery's protection circuit has locked out and won't pass current to the remote's logic board. A replacement cell arrives at a partial charge above that threshold and initialises correctly on first connection. Fit the new battery, seat the connector fully, and place the remote on its dock for at least 30 minutes before testing.