About this replacement
WITT Oxybaby — 3.6V Ni-MH Replacement Battery (850011100)
This is a 3.6V, 2000mAh Ni-MH replacement battery for the WITT Oxybaby portable oxygen concentrator. It fits the Oxybaby unit directly, restoring battery-powered operation for patients using the device during transport or away from mains power. Capacity is rated at 7.2Wh, matching the original pack specification.
- Oxybaby platform fit: The Oxybaby runs a single-cell Ni-MH pack at 3.6V nominal. The BMS in this unit monitors cell voltage directly — cell chemistry, voltage rail, and connector must match the OEM spec exactly, or the device will not register the pack as valid. This replacement uses the same voltage profile and connector footprint as part 850011100.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on a Ni-MH-compatible analyser. The BMS accepted the cell without error, and voltage held within expected range under simulated sustained load — consistent with what the Oxybaby oxygen delivery circuit draws during active use.
- First-use conditioning on the Oxybaby: Ni-MH cells shipped in storage state often read falsely low on the device's battery indicator for the first one to two cycles. Run the Oxybaby until the low-battery alert triggers, then charge fully — the unit recalibrates its voltage threshold to the new cell after one complete cycle.
Why the Oxybaby stops delivering oxygen mid-session on a seemingly charged pack
The Oxybaby's BMS uses a voltage floor to protect the cell — when terminal voltage drops below that threshold under load, the device cuts output before the displayed charge reads zero. An aged or deeply discharged Ni-MH cell has higher internal resistance, so voltage sags sharply the moment the oxygen delivery circuit draws current. The result looks like a sudden shutdown from a "charged" battery. A new cell with lower internal resistance sustains voltage above the cutoff threshold throughout the session, so the device completes delivery cycles without interruption.
Pack will not charge after the Oxybaby sat unused for several months
Ni-MH cells self-discharge during storage — after several months unused, cell voltage can drop below the charger's detection floor, and the Oxybaby's charging circuit will not initiate a charge cycle if it reads the pack as non-recoverable. This is a BMS sleep state, not a dead cell. To recover, connect the device to mains power and leave it on charge for 30 to 60 minutes without powering it on — some chargers require a trickle pre-charge phase before the main charge cycle begins. If the charge indicator does not activate after that window, check that cell voltage is above 1.0V using a multimeter at the pack terminals.