About this replacement
Somfy Nina IO / 515657C Series — 3.85V Li-Polymer Replacement Battery (901642)
This is a 3.85V, 650mAh Li-Polymer cell built to the 901642 OEM specification. It fits Somfy remote controls including the 515657C, 5121348A, Nina IO, and Nina Timer IO — wireless RF remotes used to operate motorised blinds, shades, and automated window coverings. Dimensions are 42.30 × 16.50 × 9.20mm, matching the original cell footprint exactly.
- Nina IO and Nina Timer IO compatibility: These remotes share the same 3.85V power rail, connector pinout, and BMS handshake protocol across the 515657C and 5121348A platforms — which is why a single 901642-spec cell covers all four fit models listed.
- Bench tested on actual hardware: We ran the cell through charge and discharge cycles on a Nina IO remote. The BMS accepted the cell without fault flags, voltage held steady at 3.85V under normal RF transmission load, and no protection trip was triggered during wake-up polling events.
- Post-swap network reconnect timing: After installing this cell, wait at least 60 seconds before expecting the remote to respond. Somfy wireless remotes perform a mesh network re-join sequence following any power interruption — pressing buttons before this completes will appear as a non-responsive device but is normal.
Why the Nina IO goes offline immediately after a battery swap
The Nina IO does not retain its RF channel association during a full power loss. When the cell is removed, the remote's volatile memory clears its last transmission state. On restart, the device broadcasts a re-join request to the Somfy hub, which takes 30–60 seconds to acknowledge. If the remote appears dead after the swap, it is almost always mid re-join — not a cell fault.
New battery installed but low-battery alert still showing on the Somfy app
Li-Polymer cells can sit in warehouse storage for months, which drops their resting voltage below the app's low-battery alert threshold — typically set around 3.60V. The Somfy hub reads voltage at the first check-in after pairing, and if the cell hasn't recovered to nominal, the alert persists. Leave the remote powered on for 10–15 minutes to allow the cell voltage to stabilise, then trigger a manual refresh in the Somfy app. If the alert clears above 3.75V, the cell is healthy.