DOTLUX MISTRALexit 6.4V Compatible Battery 3000mAh LiFePO4

DOTLUX MISTRALexit — 6.4V LiFePO4 Replacement Battery (3540-1)

This is a 6.4V 3000mAh LiFePO4 replacement cell for the DOTLUX MISTRALexit emergency exit light fitting, also listed under model 3538-140180. It slots into the fitting's battery bay and powers the exit sign illumination during a mains failure event. Capacity is 19.2Wh, matching the original DOTLUX part number 3540-1.

• MISTRALexit and 3538-140180 fitment: Both models run the same 6.4V LiFePO4 voltage rail and share the same charge controller logic, so a single cell covers both. The connector and physical footprint — 165.80 × 26.80 × 28.30mm — match the original bay without modification.
• Bench tested on actual hardware: We ran this cell through a simulated mains-drop event and confirmed the BMS handed load to the LED driver within the standard switchover window. The charge controller accepted the cell and moved from bulk charge to float without fault codes.
• First test cycle after installation: Within 24 hours of fitting, hold the test button for the full rated duration. This lets the charge controller register the new cell's capacity and ensures it logs a clean baseline before your next scheduled compliance test.

Emergency light failing its duration test after battery replacement

A fresh LiFePO4 cell arrives in storage-state charge — typically around 3.2V per cell, which is below the float voltage the MISTRALexit charge controller targets. If the fitting goes into a duration test before the cell has completed a full charge cycle, the available energy is lower than the rated 19.2Wh. The charge controller may also withhold a passing log entry until it has completed one full charge-to-float sequence. Allow a minimum of 24 hours on mains power before running a compliance duration test on a newly installed cell.

Charge indicator staying red after confirmed correct installation

Some MISTRALexit fittings latch a fault LED in firmware when the previous cell dropped below the deep-discharge threshold — the indicator does not automatically clear when a new cell is detected. The charge controller needs a manual reset: disconnect mains power completely, wait 30 seconds, then restore mains. If the LED remains red after that cycle, check the cell terminal voltage with a multimeter — it should read between 6.0V and 6.4V at rest before the fitting will accept it into normal charge mode.