About this replacement
Logitech Harmony 950 / Elite — 3.7V Li-Polymer Replacement Battery (533-000128)
This 3.7V, 1300mAh lithium-polymer battery replaces the internal rechargeable cell in the Logitech Harmony 950 and Harmony Elite universal remotes (915-000260, 915-000257). The original battery is a sealed Li-Polymer pack — not a standard AA or AAA cell — that connects directly to the remote's mainboard via a JST-style connector. When charge capacity drops noticeably, this replacement restores full operation.
- Harmony 950 and Elite compatibility: Both remotes share the same internal battery bay dimensions, connector pinout, and 3.7V nominal voltage rail. The BMS on each unit reads the same charge curve, so one replacement cell covers both models without modification.
- Bench tested on actual hardware: We ran this cell through full charge cycles on the Harmony 950 mainboard. The BMS accepted charge without fault codes, hit the correct 4.2V cutoff at full charge, and held resting voltage at 3.7V under standby load.
- Connector seating on the Harmony 950: The JST connector on this remote sits in a recessed housing. Press the connector straight down — do not angle it in. A partially seated connector causes the remote to power on briefly then cut out, which looks like a dead cell but is a contact fault.
Why the Harmony 950 screen turns on but IR blasting stops working
The Harmony 950 drives up to 40 IR emitters in some configurations, which draws a short burst of current well above standby levels. A degraded or partially charged Li-Polymer cell can maintain enough voltage to run the display but sag below the threshold needed to fire the IR LED array. This is a voltage-sag failure, not a total battery failure. A fresh cell at full charge eliminates the sag — confirm the replacement reads 4.1V or above before installing.
Harmony Elite showing "charging" continuously without reaching full charge
If the Harmony Elite sits on its charging base and never exits the charging state, the original Li-Polymer cell has likely lost enough capacity that the BMS cannot confirm a full charge cycle completes. The charging circuit keeps topping up a cell that drains faster than it charges. Replace the battery, then seat the remote on the base for a full uninterrupted charge until the indicator clears — typically confirmed when resting voltage holds at 4.1–4.2V off the charger.