Franklin Celltron Ultra Replacement Battery 9.6V 2000mAh

Franklin Celltron Ultra / Grid C090 Ultra — 9.6V Ni-MH Replacement Battery (125-0036)

This is a 9.6V, 2000mAh Ni-MH replacement battery for the Franklin Celltron Ultra and Grid C090 Ultra professional surveying and testing instruments. It matches OEM part numbers 125-0036 and 125-0036 REV C. Voltage and cell count are identical to the original pack.

• Celltron Ultra and Grid C090 Ultra compatibility: Both instruments share the same 9.6V eight-cell NiMH architecture and connector pinout. The battery management handshake uses the same thermal cutoff line, so one pack covers both platforms without modification.
• Bench tested on actual hardware: We cycled this pack through the Celltron Ultra's instrument-side charge controller and confirmed the thermistor line communicates correctly at all three charge stages. The BMS held cutoff at the correct peak-delta-V threshold across repeated cycles.
• Post-install calibration cycle: After fitting this pack, run a full calibration sequence through the instrument menu before field deployment. The Celltron Ultra maps battery state during calibration — skipping this step causes the low-battery warning to trigger early on the first measurement session, even with a full charge.

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

NiMH cells self-discharge at roughly 1–2% per day at room temperature. After several months in storage, the pack voltage can drop below the BMS recovery threshold — typically around 7.2V on a 9.6V pack — and the protection circuit latches off. The instrument either shows nothing on power-up or briefly flickers and shuts down. To recover, connect the pack to a NiMH-capable charger that supports a trickle pre-charge mode; this brings cell voltage up slowly until the BMS re-initialises, usually within 20–40 minutes of trickle current at 0.1C.

Celltron Ultra shutting down the moment a probe or sensor module initialises

Probe modules draw a short current spike at power-up as their internal circuits initialise — on the Celltron Ultra this can briefly exceed the BMS overcurrent threshold on a partially discharged or cold pack. The BMS interprets this spike as a fault and cuts output, even though the battery itself has adequate charge remaining. Cold temperatures make this worse because NiMH internal resistance rises sharply below 10°C. Bring the instrument to room temperature before powering on, and ensure the pack is above 9.0V before connecting an external probe module.