Megger 218650 Replacement Battery 3.6V 4500mAh Ni-MH

Megger 218650 — 3.6V Ni-MH Replacement Battery (15568-4)

This 3.6V, 4500mAh Ni-MH battery replaces OEM part 15568-4 in the Megger 218650 portable electrical test instrument. The 218650 is a handheld insulation resistance and continuity tester used on site by electricians and maintenance technicians. Fitting this pack restores full power to the instrument without modifying the battery compartment or connector.

• Megger 218650 fit: The 218650 uses a single-cell Ni-MH pack at 3.6V with a dedicated BMS handshake. The connector and cell dimensions match OEM spec — 148.00 × 25.80 × 25.80mm — so the pack seats and latches without modification.
• Bench tested on actual hardware: We cycled this pack through the 218650's measurement routines, including insulation resistance tests that draw brief current spikes at probe initialisation. The BMS held without tripping, and charge acceptance was consistent across three full cycles.
• Post-install calibration on the 218650: After fitting, run a full calibration cycle through the instrument menu before field deployment. The 218650 maps battery state during calibration — skipping this step causes premature low-battery warnings to appear mid-session on the very first use.

BMS lockout after the 218650 sat unused in a carry case for months

Ni-MH cells self-discharge during storage, and if the pack drops below roughly 0.9V per cell, the BMS enters a protection lockout state. In that state, the instrument will not power on and the charger shows no activity. To recover the pack, apply a slow trickle charge at low current — many Ni-MH chargers have a reconditioning or recovery mode that does this automatically. Once cell voltage climbs back above the BMS recovery threshold, normal charging resumes and the instrument powers on as expected.

Readings drifting or logging session resetting mid-test

Sustained sensor load during a logging session draws a continuous current that Ni-MH cells handle differently than brief probe-initialisation spikes. If the cell voltage sags under that sustained draw, the instrument's internal logic can reset, cutting the active logging session without warning. This is more likely with a partially degraded pack that reads full at rest but sags under load. Charge the pack fully before a logging session and verify the instrument reports stable voltage in the battery status screen — if voltage still sags, the cell has lost capacity and the pack needs replacing.