Sonel CMM-60 Replacement Battery 7.4V 2400mAh Li-Polymer

Sonel CMM-60 Multimeter — 7.4V Li-Polymer Replacement Battery (WAAKU25)

This is a 7.4V, 2400mAh Li-Polymer battery for the Sonel CMM-60 portable digital multimeter. It replaces OEM part numbers WAAKU25, AKU-25, and 534296-2S. The CMM-60 uses this pack as its sole power source during electrical measurement and survey work in the field.

• CMM-60 compatibility: The CMM-60 runs a 7.4V two-cell Li-Polymer architecture with a specific connector pinout and BMS handshake. This pack matches that voltage rail and connector geometry exactly — the BMS communication lines align, so the instrument reads cell state correctly rather than throwing a battery fault.
• Bench tested on actual hardware: We cycled this pack through the CMM-60's measurement modes, including sustained continuity testing and AC voltage measurement under load. The BMS held the output rail stable and did not trip under the probe initialisation current spike typical of this instrument.
• Post-install calibration step: After fitting this pack, run a full calibration cycle through the CMM-60's instrument menu before taking it into the field. The CMM-60 maps battery state during calibration — skipping this step causes premature low-battery warnings to appear during the first measurement session even when the pack is fully charged.

CMM-60 shutting down mid-measurement with the battery indicator showing charge

The CMM-60's BMS has a current-spike threshold that can trip during probe module initialisation — particularly when switching to current clamp or capacitance mode mid-session. When the original pack ages, its internal resistance rises and the voltage sags sharply under that initialisation spike, which crosses the BMS cutoff threshold even though the resting voltage looks healthy. A new pack at lower internal resistance handles the spike without the voltage sag. If the shutdown persists after fitting a new pack, check that the probe leads are fully seated before powering on — a partial connection forces the instrument to re-initialise the probe circuit and repeat the spike.

CMM-60 not recognising a new pack after the instrument sat unused for months

Li-Polymer cells self-discharge during storage, and if the pack voltage drops below approximately 2.5V per cell (5.0V total), the BMS enters a sleep state and stops responding to the charger. The CMM-60 will power on briefly or not at all, and the charging indicator may not light. To recover the pack, connect it to a Li-Po compatible charger with a recovery or trickle mode and let it run at low current — typically 100mA — until the pack voltage climbs above 6.0V. Once above that threshold, the BMS wakes and normal charging resumes.