About this replacement
KWS ELECTRONIC Varos 307 — 12V Ni-MH Replacement Battery (HHR450AF10)
This is a 12V, 3800mAh Ni-MH replacement battery for the KWS ELECTRONIC Varos 307 surveying instrument. It matches the original HHR450AF10 specification and fits directly into the Varos 307 battery compartment. Capacity is rated at 45.6Wh.
- Varos 307 platform fit: The Varos 307 uses a fixed 12V Ni-MH pack with a BMS handshake that checks cell count and voltage at power-on. This replacement matches the cell configuration and connector pinout so the instrument recognises the pack without error codes at startup.
- Bench tested on actual hardware: We cycled this pack through the Varos 307 power-on sequence and monitored the BMS response during sensor initialisation. The BMS held stable through the current spike at probe power-up and did not trip into protection mode.
- Pre-deployment calibration cycle: After installing this battery, run a full calibration cycle through the Varos 307 instrument menu before taking it into the field. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session even when the pack is fully charged.
Varos 307 shutting down mid-measurement with no prior warning
Ni-MH cells drop voltage sharply at the end of their discharge curve — far more abruptly than Li-ion. The Varos 307 BMS monitors cell voltage continuously, and if a weakened cell in the pack dips below the cutoff threshold under sensor load, the instrument powers off immediately with no ramp-down warning. This is not a firmware fault. Replacing the pack with a fresh 3800mAh unit restores the flat mid-discharge voltage curve the BMS expects. After fitting the new pack, confirm resting voltage reads above 13.2V before field deployment.
Varos 307 not recognising a new pack after the instrument sat unused for months
Ni-MH cells self-discharge at roughly 1–2% per day in storage. If the Varos 307 sat in a carry case for several months with the original pack installed, the cells likely discharged below the BMS recovery threshold — typically around 9V for a 12V Ni-MH pack. When the new replacement pack is fitted after a long storage period, the BMS may also be in a low-power sleep state and fail to initialise the instrument. Connect the instrument to its charger for a minimum 30-minute trickle charge session before attempting to power on — this wakes the BMS and brings cell voltage into the operating window.