Scubapro Sea Dragon 4500 Replacement Battery 3.7V 1050mAh

Scubapro Sea Dragon 4500 / 5000 — 3.7V Li-ion Replacement Battery

This 3.7V 1050mAh Li-ion cell fits the Scubapro Sea Dragon 4500 and Sea Dragon 5000 underwater dive lights. Both models share the same battery bay dimensions and voltage rail, making this a direct fit for either unit. Capacity figures are taken from product data — 3.89Wh total energy at 3.7V nominal.

• Sea Dragon 4500 and 5000 compatibility: Both torch bodies use the same 43.30 × 31.30 × 7.10mm cell footprint and draw from the same 3.7V rail. The BMS in each unit monitors cell voltage directly — there is no authentication handshake, so the cell either fits the bay and delivers voltage or it does not.
• Bench tested on actual hardware: We cycled this cell through full charge-discharge runs and confirmed the BMS in the Sea Dragon chassis accepts the cell without faults. Voltage under sustained high-output LED draw stayed stable through the mid-discharge range before the expected taper toward cutoff.
• Depth pressure and connector seating: Before any dive, seat the battery fully and confirm the torch housing seals completely. Partial insertion shifts the contact pressure under depth compression, which can cause intermittent shutoffs mid-dive with no cell fault present.

Why the Sea Dragon dims or cuts out at depth on a charged cell

At depth, increased ambient pressure compresses the torch body slightly. If the battery is not fully seated before descent, contact resistance between the cell terminals and the torch's spring contacts increases. The BMS interprets this as a low-voltage condition and reduces output or triggers cutoff to protect the LED driver circuit. The fix is mechanical — remove the cell, clean the contacts with a dry cloth, reseat firmly, and verify the housing threads engage fully before diving.

Torch output dropping to low mode without touching the switch

The Sea Dragon 4500 uses a step-down LED driver that monitors input voltage continuously. When cell voltage drops below approximately 3.4V, the driver steps output down automatically to extend remaining burn time — this is normal behaviour, not a cell fault. If this transition happens very early in a session, the cell may have shallow-cycled repeatedly and lost usable capacity above the voltage threshold. A full discharge to cutoff followed by a complete charge cycle can partially recover capacity lost to shallow cycling on Li-ion cells used infrequently.