About this replacement
Ascom Myco SH1 Series — 3.7V Li-ion Replacement Battery (490926A)
This is a 3.7V, 1750mAh Li-ion battery for the Ascom Myco wireless handset. It fits the Myco, Myco SH1 VoWiFi, SH1-ABAA, and SH1-ABAA/F models used in hospital and clinical communication systems. Also cross-references OEM part RB-490926-LW.
- Myco SH1 platform compatibility: The SH1-ABAA and SH1-ABAA/F share the same 3.7V battery bay, connector pinout, and BMS handshake protocol. One cell fits all four model variants without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on an SH1 handset. The BMS accepted the cell on first insertion, completed voltage verification, and held the charge curve within the expected range for Li-ion at this capacity.
- Post-swap self-test protocol: After installing this battery, let the Myco complete its full power-on self-test without pressing any keys or interrupting the boot sequence. The BMS runs a chemistry verification step at startup. Interrupting it logs a false battery fault that persists until the next full reboot.
Why the Myco alarms low battery immediately after a confirmed full charge
The Myco's BMS stores learned thresholds calibrated to the original cell's charge curve. A new cell with a slightly different internal resistance profile can read below the BMS alarm threshold on the first cycle, even at full charge. This is not a fault with the replacement cell. Run one complete charge-discharge cycle and the BMS recalibrates its reference points. The low-battery alarm clears after that first full cycle completes.
Myco handset will not power on after the battery sat in storage
Li-ion cells self-discharge over time. If this battery was stored for several months before installation, its resting voltage may have dropped below the Myco's BMS recovery threshold — typically around 2.5V for this chemistry. The handset will not attempt to boot below that threshold as a protection measure. Place the handset on charge for at least 30 minutes before pressing the power button, giving the charge IC enough time to bring the cell above the minimum recovery voltage before the BMS re-enables the output rail.