Honeywell Lynx L3000 7.2V Replacement Battery 1500mAh

Honeywell Lynx L3000 / L5100 Series — 7.2V Ni-MH Replacement Battery (300-03864-1)

This is a 7.2V, 1500mAh Ni-MH backup battery for the Honeywell Lynx L3000, L5000, L5100, and K5109 security panel series. It maintains power to the control panel during mains outages, keeping the alarm armed and communication with monitoring stations active. Capacity is 10.8Wh, matching OEM specifications.

• Lynx L3000 / L5000 / L5100 / K5109 compatibility: These panels share the same 7.2V battery bay, connector pinout, and float-charge circuit. The BMS on each model monitors cell voltage and flags a low-battery fault below a set threshold — this cell meets that voltage requirement at full charge.
• Bench tested on actual hardware: We ran this cell on a Lynx L5100 panel. The BMS accepted the battery, cycled through float charge without tripping a fault, and cleared the low-battery warning within 36 hours of continuous charge.
• First-charge protocol for alarm panels: Do not run a zone or siren test immediately after swapping this cell. Allow 24–48 hours on float charge before triggering any diagnostic test. Running a test too early will draw the cell below the panel's reporting threshold and generate a false low-battery alert.

Why the Lynx L3000 reports low battery within hours of a new cell install

The Lynx panel measures battery voltage continuously and compares it against a fixed threshold — typically around 6.8V for a 7.2V Ni-MH cell. A brand-new cell sitting at partial charge from storage can read below that threshold immediately after installation. The panel then logs and displays a low-battery fault, which is not a cell defect. Leave the panel on mains power for 24–48 hours. Once float charge brings the cell above the threshold voltage, the fault clears automatically.

Alarm panel loses all programming during a mains outage after battery replacement

If the panel loses zone settings, user codes, or installer configuration during a power cut, the backup battery was not yet fully conditioned at the time of the outage. A partially charged Ni-MH cell drops voltage quickly under the load of powering the processor and communication module. The panel interprets this as a full power loss and resets to factory defaults. Install the new cell, keep the panel on mains for a full 48 hours before the next power interruption, and confirm battery voltage reads at or above 7.2V before running any outage test.