Land Rover Discovery 5 Emergency Power 4V 1200F Battery

Land Rover Discovery 5 2017-2020 — 4V HPC Replacement Supercapacitor Battery

This is a 4V, 1200F (4.8Wh) HPC supercapacitor replacement for the emergency power supply unit fitted to the Land Rover Discovery 5 (2017–2020) and Discovery Sport (2015). It backs up critical vehicle electronics — remote locking, alarm systems, and safety-critical functions — during main battery failure or power loss. Dimensions are 50.20 x 28.60 x 14.60mm.

• Discovery 5 and Discovery Sport fitment: Both models share the same emergency power supply architecture, voltage rail, and supercapacitor form factor. The 4V HPC cell interfaces directly with the vehicle's emergency power management module using the same connector and BMS handshake protocol across these platforms.
• Bench tested on actual hardware: We ran this supercapacitor through charge and discharge cycles on the bench. The BMS accepted the cell without fault codes, held voltage within spec under simulated emergency load, and completed the self-test sequence cleanly.
• Post-installation charge cycle requirement: The Land Rover emergency power module will not trust the cell's energy estimate until it completes at least one full charge cycle post-installation. Run the vehicle with the ignition on for a full charge period before relying on emergency functions — the module's self-test will not pass until this is done.

Why the emergency supply module rejects a new supercapacitor on first installation

The Discovery 5 emergency power module runs a BMS handshake when a new cell is detected. It checks capacitance, internal resistance, and resting voltage before it marks the unit as operational. A freshly installed supercapacitor may sit below the module's acceptance threshold if it discharged during storage. The module will log a fault and hold the unit in a non-operational state until the cell reaches full charge — typically 4V at the cell terminals. Allow a full charge cycle before expecting the self-test to clear.

Emergency supply self-test failure after battery swap

After a supercapacitor swap, the module's calibration routine requires a complete charge-discharge cycle to recalibrate its energy estimate. If the self-test runs before the cell is fully charged, it will fail — not because the cell is faulty, but because the management firmware hasn't yet validated the cell's capacitance at full charge. Leave the vehicle on charge for a minimum of two hours after installation, then trigger the self-test again. The module expects to read at least 3.8V at the cell before it will pass the test sequence.