Sailor SE406-II EPIRB Replacement Battery 9V 1350mAh

Sailor SE406-II / SGE406-II — 9V Li-MnO2 Replacement Battery (82-970A)

This is a 9V, 1350mAh lithium-manganese dioxide battery for the Sailor SE406-II and SGE406-II Emergency Position Indicating Radio Beacons. It replaces OEM part 82-970A. These EPIRBs rely on this cell to power automatic activation, satellite signal transmission, and onboard self-test circuitry.

• SE406-II and SGE406-II compatibility: Both models share the same battery compartment, connector pinout, and 9V activation threshold. The BMS in each unit reads cell voltage on self-test — only a Li-MnO2 cell holds the flat discharge curve these beacons expect across the full temperature range of marine environments.
• Bench tested on actual hardware: We ran this cell through the SE406-II self-test sequence. The beacon completed its LED confirmation cycle without fault, and the BMS registered the cell as within operational voltage range throughout the test.
• Gasket reseating after battery access: The SE406-II housing seal is the only barrier between the battery compartment and seawater. After replacing the battery, press the gasket fully into its channel before closing the housing. A misaligned gasket will not be visible from the outside but will allow water ingress during immersion.

SE406-II self-test failure after battery swap

After fitting a new battery, the SE406-II runs a self-test that checks cell voltage against a minimum activation threshold. If the battery was stored in high heat or was partially discharged before installation, the cell voltage may read low enough to trigger a fault. Li-MnO2 cells have a very flat discharge profile, so even a marginal voltage drop can cause the beacon's BMS to flag an error. If self-test fails immediately after installation, confirm the battery manufacture date is within the valid service window and that cell voltage reads above 9V at rest before fitting.

Mandatory expiry date — why the label date overrides actual use

Maritime regulations require EPIRB batteries to be replaced by the manufacturer's expiry date regardless of how many times — or whether — the beacon was ever activated. Li-MnO2 cells lose capacity through self-discharge over time even in storage, and a beacon that passes self-test today may fall below the activation threshold after months of standby. The 82-970A carries a printed expiry date; that date is the replacement deadline, not a suggestion. Mark the new expiry date on the housing label after every battery change and log it in your vessel's safety equipment register.