About this replacement
Minelab Excalibur 800 Series — 12V Ni-MH Replacement Battery (TER51140)
This is a 12V, 1400mAh Ni-MH replacement battery for the Minelab Excalibur 800 Metal Detector and related Excalibur series detectors. It replaces OEM part TER51140 directly. The Excalibur line is a waterproof underwater detector — this battery powers the unit during beach, surf, and freshwater prospecting sessions.
- Excalibur 800, Excalibur II, Excalibur 1000, and Excalibur II PODS: These models share the same 12V battery bay, connector pinout, and charge circuit. One pack fits all variants without modification.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on the Excalibur platform. The BMS held stable across full draw cycles, and the charge circuit accepted the pack without fault codes or cutoff interruptions.
- Post-install charge cycle on the Excalibur: After fitting a new pack, run a complete charge using the Minelab charger before entering the water. The Excalibur's charge circuit calibrates to the pack's internal resistance on the first full charge — skipping this causes early low-battery indicators during your first search session.
Why the Excalibur powers off suddenly after months of storage
Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A pack stored for three or more months can drop below the BMS recovery threshold — typically around 9V on a 12V Ni-MH pack. When the detector powers on, the BMS sees a cell voltage too low to sustain load and cuts output within seconds. The fix is a slow pre-charge at low current before a full charge cycle. Most Minelab chargers will handle this automatically if left connected — allow at least 12 hours on the charger before testing the unit.
Excalibur shuts down mid-sweep with no warning indicator
This typically happens when aged cells can no longer hold voltage under the sustained draw of the detector's coil and signal processing circuit. The pack may read as charged at rest, but voltage sags below the cutoff threshold the moment the coil energises. It is not a charger fault. Test resting voltage at the battery terminals — a healthy 12V Ni-MH pack should read at least 12.5V fully charged. If resting voltage is below 11.8V after a full charge cycle, the pack has reached end of life and needs replacement.