Fluke DTX-LION 7.4V 5200mAh Replacement Battery

Fluke DTX-1200-M / DTX-1800-M Series — 7.4V Li-ion Replacement Battery (DTX-LION / BP7440)

This 7.4V, 5200mAh Li-ion battery replaces the OEM DTX-LION and BP7440 packs in Fluke DTX-1200-M, DTX-1200-MS, DTX-1800-M, and DTX-1800-MS cable analyzers. These units are handheld copper and fiber certification testers used in the field where mains power is unavailable. Capacity is 5200mAh (38.48Wh) — drawn from product data, not estimated.

• DTX-1200-M and DTX-1800-M series fit: All four models share the same 7.4V battery bay, connector pinout, and BMS communication protocol. The DTX-1200-MS and DTX-1800-MS are the Smart Remote variants — they draw from the same battery circuit, so one replacement pack covers the full platform.
• Bench tested on actual hardware: We ran this pack through the DTX power-on sequence, full link calibration, and a sustained Cat 6A certification sweep. The BMS negotiated correctly with the instrument firmware, held stable voltage under the measurement processor load, and accepted a full charge cycle without faults.
• Calibration cycle before first field deployment: After fitting this pack, run a full calibration cycle through the DTX instrument menu before taking it to site. The DTX maps battery state during calibration — skip this step and the unit will flag low-battery warnings well before the pack is actually depleted on your first measurement session.

DTX-1800-M shutting down mid-sweep during high-pair-count certification runs

The DTX-1800-M draws a short current spike each time it fires the measurement signal across a new pair combination during an Autotest. On a depleted or aged cell, that spike pulls the pack voltage below the BMS protection threshold, triggering a cutoff. The instrument interprets this as a hard power loss, not a battery warning — so you see an abrupt shutdown rather than a low-battery icon. A fresh 5200mAh cell maintains enough voltage headroom to absorb these spikes without tripping the BMS cutoff.

DTX showing inconsistent charge percentage at every reboot

The DTX series reads state of charge from a voltage-threshold table stored in firmware. A new cell has slightly different resting voltage characteristics than the original OEM pack the instrument was calibrated against. Until the DTX has seen at least one full charge-to-discharge cycle on the new pack, its percentage display will jump — commonly showing 40% at boot then climbing to 80% after a few minutes of use. Run one complete cycle: charge to full, run through a calibration sweep and a full Autotest session, then recharge. After that cycle, the percentage reading stabilises to within a few percent of actual state of charge.