About this replacement
Honda Car Immobiliser — 7.2V Ni-MH Replacement Battery (37110-SMG-E012-M1)
This 7.2V Ni-MH cell replaces the backup battery in Honda car immobiliser systems using OEM part number 37110-SMG-E012-M1. It powers the alarm and immobiliser backup circuit when main vehicle power is lost. Capacity is 230mAh (1.66Wh), matching the original specification exactly.
- Honda immobiliser backup circuit: The immobiliser module draws from this cell only when the vehicle's main 12V supply drops — during battery disconnection or a dead main battery. The BMS in the module expects a 7.2V Ni-MH pack at this exact cell count. Substituting a different voltage or chemistry causes the module to reject the backup source entirely.
- Bench tested on actual hardware: We ran this cell on the bench against the immobiliser module's charge circuit. The BMS accepted the pack at first connection, initiated trickle charge immediately, and showed no fault codes during the float phase.
- Post-installation float charge window: Do not trigger a full alarm or immobiliser test within the first 48 hours after fitting. The module charges this cell via trickle only — running a system test before float charge completes may cause the panel to log a low-battery fault even with a fresh cell installed.
Why the Honda immobiliser panel still shows low battery after fitting a new cell
The immobiliser module does not switch the backup battery status flag the moment a new cell is connected. It samples backup voltage on a timed cycle — typically every few hours — and only clears the low-battery fault once it confirms the cell has reached float voltage through the module's own trickle charge circuit. A freshly installed Ni-MH cell at resting voltage sits below the module's acceptance threshold. Leave the vehicle with ignition-off power connected for 24–48 hours, then check the fault log again.
Immobiliser losing stored programming during a main battery swap
If the backup cell is depleted when you disconnect the main 12V battery, the immobiliser module loses its volatile memory — key fob pairings, alarm zone configuration, and sometimes the PIN sequence. This happens because the backup cell voltage has dropped below the module's memory-hold threshold of approximately 6V. Fit and condition this replacement cell first, confirm float charge is complete, then disconnect the main battery for your swap. After reconnecting, the module should retain all stored programming.