About this replacement
Micro Medical MicroLoop 3535 Spirometer — 3.6V Ni-MH Replacement Battery (BAT6709)
This is a 3.6V, 1200mAh Ni-MH rechargeable battery for the Micro Medical MicroLoop 3535 Spirometer. It replaces OEM part BAT6709 in the portable handheld spirometer used for pulmonary function testing in clinical and home healthcare environments. Dimensions are 51.30 × 30.00 × 17.30mm — confirm these against your existing cell before installing.
- MicroLoop 3535 fitment: The 3535 runs a 3.6V single-cell Ni-MH architecture. The BAT6709 cell matches the voltage rail and physical connector that the device's charge management circuit expects. Substituting a different chemistry or voltage will trigger charge faults.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench and monitored the BMS handshake. The protection circuit held cutoff correctly at both ends, and charge termination triggered cleanly at capacity.
- Power-on self-test after swap: After installing this cell, allow the MicroLoop 3535 to complete its full power-on self-test without interruption. The device runs a BMS verification sequence at startup — cutting power mid-cycle flags a false battery fault that will persist until the next complete reboot.
Why the MicroLoop 3535 shows a battery fault after the first charge
The MicroLoop 3535's charge IC applies a conservative acceptance threshold calibrated to an aged OEM cell. A brand-new Ni-MH cell has a slightly different internal resistance profile at first, and the charge circuit can misread this as a fault condition. This typically clears after one complete charge-discharge cycle. Run the device through a full session to discharge the cell, then charge to completion before using it in a clinical context.
Charge indicator not reaching 100% on the first charge cycle
New Ni-MH cells often show an incomplete charge on the first cycle — the charge IC applies a reduced current limit until it has profiled the cell's delta-V response. The display reads below full even though the cell has accepted a normal charge. Run one full charge-discharge cycle and the indicator will read correctly from the second charge onward. If it still fails to reach full after three cycles, check terminal voltage directly — a healthy cell at full charge will sit at approximately 1.4V per cell, or 4.2V across this pack.