About this replacement
Bticino OVA51104 Emergency Lighting Unit — 2.4V Ni-Cd Replacement Battery (MGN0916)
This is a 2.4V, 800mAh Ni-Cd replacement battery for the Bticino OVA51104 emergency lighting unit. It also fits the 806312, L4784/1, and 789798 variants that share the same battery bay and charge controller. The MGN0916 cell restores backup illumination function when the original cell has degraded beyond the unit's charge threshold.
- OVA51104 / 806312 / L4784/1 / 789798 fit group: These models share the same 2.4V charging rail, physical form factor (50.90 × 28.50 × 14.30mm), and two-wire connector orientation. Any unit in this group that accepts MGN0916 will accept this cell without modification.
- Bench tested on actual hardware: We ran the cell through the OVA51104's charge controller and confirmed the BMS accepted float charge within the expected window. The unit cleared its self-test LED sequence and registered a full charge state.
- First test cycle after installation: Within 24 hours of fitting, hold the manual test button for the full rated duration. This allows the charge controller to register the new cell's capacity before any scheduled compliance test — a cell that hasn't completed one full load cycle will under-read on formal duration tests.
Why the OVA51104 charge indicator stays red after fitting a new cell
Ni-Cd cells lose voltage during storage, and the OVA51104's charge controller uses a float acceptance window to decide whether to enter charge mode. A cell that arrives below roughly 2.0V may sit outside that window and hold the red LED on. The controller isn't faulty — it's waiting for the cell voltage to rise above the acceptance threshold before switching to charge mode. In most cases, leaving the unit on mains power for 12 to 24 hours allows the cell to self-recover enough voltage to enter the charge cycle. If the LED hasn't shifted to green after 24 hours, check the cell seating and connector contact first.
Emergency light dims or cuts out partway through a duration test
A new Ni-Cd cell that hasn't completed its first full charge-discharge cycle will not deliver rated capacity on the initial load test. The cell may reach cutoff voltage earlier than expected, causing the light to dim or drop out before the test duration ends. This isn't a faulty cell — it's normal Ni-Cd behaviour on the first cycle. Run one full manual test cycle after 24 hours on charge, and the cell will condition to its rated 800mAh capacity for subsequent compliance tests.