Horizon Kronos C3+ Replacement Battery HKB10 7.4V 3400mAh

Horizon Kronos C3+ — 7.4V Li-ion Replacement Battery (HKB10)

This is a 7.4V 3400mAh Li-ion replacement battery for the Horizon Kronos C3+ surveying and testing instrument. It replaces OEM part HKB10 and fits the Kronos C3+ directly. Capacity is 3400mAh (25.16Wh), matching the original cell specification.

• Kronos C3+ compatibility: The C3+ uses a fixed 7.4V two-cell Li-ion architecture with a BMS handshake tied to cell voltage and pack geometry. This replacement matches the original connector pinout and pack dimensions (70.35 × 38.50 × 20.65mm), so the instrument recognises the pack and communicates state-of-charge without firmware flags.
• Bench tested on actual hardware: We cycled this pack through the Kronos C3+'s probe initialisation sequence, which draws a short current spike as sensor modules power up. The BMS held the rail steady through that event and did not trip into protection mode.
• First-use calibration cycle: After installing this pack, run a full calibration cycle through the instrument menu before field deployment. The Kronos C3+ maps battery state during calibration — skipping this step causes premature low-battery warnings on your first measurement session, even when the pack is fully charged.

BMS lockout on the Kronos C3+ after the pack sat unused for months

Li-ion cells self-discharge slowly in storage. If the Kronos C3+ sat in a carry case for several months with the original pack still inside, cell voltage can drop below the BMS recovery threshold — typically around 2.5V per cell for a 7.4V two-cell pack. At that point the BMS enters a deep-sleep lockout and will not respond to a standard charger. To recover the pack, apply a slow pre-charge at a reduced current (often called a "trickle" or "recovery" mode on a lab charger) until cell voltage climbs above 2.8V per cell, then switch to normal charge. If the pack does not respond after 15–20 minutes of pre-charge, the cells have degraded past recovery and the pack needs replacing.

Readings resetting or dropping out during a logging session

This symptom is different from a full shutdown — the instrument stays on but logged values reset or sensors briefly drop signal. The cause is a momentary voltage sag under sustained sensor load: as the instrument logs continuously, combined draw from the processor, display, and active sensor modules pulls the rail low enough to trigger a brown-out reset in the measurement circuit. A pack with degraded cells cannot hold voltage steady under that sustained draw, even if the charge indicator looks healthy. Replace the battery and confirm the resting cell voltage is above 3.7V per cell (7.4V total) before the next logging session.