Fieldpiece RLB2 SRL2 Replacement Battery 3.7V 1800mAh

Fieldpiece SRL2 / SRL8 Leak Detectors — 3.7V Li-ion Replacement Battery (RLB2)

This 3.7V, 1800mAh Li-ion battery replaces the OEM RLB2 pack in Fieldpiece SRL2 and SRL8 refrigerant leak detectors. It fits the same battery bay and connects to the same BMS handshake used across the SRL series. Voltage and capacity match the original spec exactly.

• SRL2 and SRL8 compatibility: Both models run the same 3.7V cell platform, share the same physical connector, and use the same BMS communication protocol — one pack covers the full SRL series without modification.
• Bench tested on actual hardware: We ran this pack through the SRL2's sensor warm-up sequence, which pulls a short current spike as the heated diode element reaches operating temperature. The BMS held the rail steady without tripping into protection mode.
• First-use calibration on the SRL2: After fitting the new pack, run a full power cycle and let the detector complete its warm-up sequence before deploying to a job site. The SRL2 maps battery state during that initialisation window — skipping it causes the low-battery indicator to trigger early on the first session, even with a full charge.

BMS cutoff during sensor element warm-up on the SRL2

The SRL2's heated diode sensor draws a sharp current spike in the first few seconds after power-on, as the element ramps to its detection temperature. A degraded or deeply discharged cell can't sustain that surge, so the BMS trips into protection mode and the unit shuts off before the ready indicator lights. This replacement pack uses cells rated to handle the warm-up inrush without dropping below the BMS cutoff threshold. If the unit still shuts off at power-on after fitting a new pack, check that the cell voltage reads at least 3.6V before first charge.

SRL8 powering on but shutting down during USB data transfer

The SRL8 combines active sensor load with USB enumeration current when transferring logs to a PC — total draw at that moment is higher than during normal scanning. If the cell voltage is already low or the pack has aged, that combined draw causes a voltage sag the BMS reads as an undervoltage fault, cutting power mid-transfer. The fix is straightforward: charge the pack fully before any data session, and verify the cell sits above 3.7V before connecting the USB cable. A pack that sags under this combined load is indicating it needs replacement, not a software fix.