Schlumberger TU89 Emergency Light Replacement Battery 6V 2000mAh

Schlumberger TU89 — 6V Ni-MH Replacement Battery

This is a 6V, 2000mAh Ni-MH replacement battery for the Schlumberger TU89 emergency lighting unit. It fits directly into the TU89 housing and restores the unit's ability to activate on mains failure. Dimensions are 52.38 x 43.46 x 27.20mm — verify against your existing cell before ordering.

• TU89 compatibility: The TU89 uses a 6V Ni-MH cell at this form factor. The charge controller in the fitting expects the voltage rise and acceptance curve of a Ni-MH pack — substituting a different chemistry or voltage will cause charge faults or overcharge damage.
• Bench tested on actual hardware: We ran this cell through a full charge cycle and a load discharge. The BMS accepted charge without flagging a fault, and the cell reached rated capacity after one complete cycle from a depleted state.
• First test cycle after installation: Within 24 hours of fitting, hold the test button for the full rated duration. This confirms the new cell accepts load under real conditions and allows the charge controller to register the new cell capacity before the next scheduled compliance test.

Why the TU89 charge indicator stays red after a new battery is fitted

A Ni-MH cell shipped in storage can sit below the float acceptance window that the TU89 charge controller expects. When the controller sees a cell voltage outside its acceptance range, it holds the fault state rather than transitioning to a charge cycle. Leave the fitting connected to mains for a full 24-hour charge before judging the indicator. If the light remains red past 24 hours, measure the cell voltage directly — it should read above 5.5V at rest to confirm the controller has accepted the pack.

Emergency light dims partway through a duration test after battery replacement

A cell that has not completed one full conditioning cycle will not deliver its rated capacity on the first test. The voltage sags under load before the cell has stabilised its electrochemical baseline. This is not a faulty cell — it is a first-cycle behaviour specific to Ni-MH chemistry. Run one complete charge-discharge cycle by performing a full manual test, then allow a full 24-hour recharge before the next compliance test.