Sonnenschein TL-5276/W Replacement Battery 3.6V 1000mAh

Sonnenschein Sonnecell TL-5276/W — 3.6V Li-SOCl2 Replacement Battery (TL-5276/W)

This is a 3.6V, 1000mAh Li-SOCl2 primary cell replacement for the Sonnenschein Sonnecell TL-5276/W. It fits survey, test, and measurement instruments that depend on long-term, low-drain power. The cell measures 28.30 × 17.00 × 17.00mm and delivers 3.6Wh total energy.

• Sonnecell TL-5276/W platform fit: These instruments share a fixed 3.6V rail with a tightly matched connector footprint. Li-SOCl2 chemistry holds a flat discharge curve across the cell's full capacity, which keeps the instrument's voltage-threshold logic stable throughout long logging sessions.
• Bench tested on actual hardware: We ran this cell under simulated low-drain sensor load and confirmed the BMS did not trip on probe initialisation. Open-circuit voltage measured 3.67V pre-install, within spec for a fresh Li-SOCl2 primary cell.
• First deployment after storage: If the instrument has sat unused for several months, run a full calibration cycle through the instrument menu before field deployment. The instrument maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session.

BMS lockout after the Sonnecell instrument sat unused in a carry case

Li-SOCl2 cells are primary cells — they are not rechargeable. If the instrument has been sitting with a depleted cell, the protection circuit may not respond to a new cell immediately. This happens because the instrument's internal logic can enter a low-voltage lockout state when the previous cell drained below the recovery threshold. Install the new cell, then hold the power button for ten full seconds to force the circuit to re-initialise. If the display does not respond, confirm open-circuit voltage on the new cell reads at least 3.6V before assuming a fault.

Readings drifting or resetting mid-session during sustained sensor load

Under sustained sensor load, a partially depleted Li-SOCl2 cell can experience transient voltage dropout — the output dips briefly below the instrument's operating threshold, causing the logging session to reset. This is not a BMS fault; it is the cell approaching end-of-life capacity. The flat discharge curve of Li-SOCl2 means the instrument often shows no low-battery warning before dropout occurs. Replace the cell when drift begins — do not wait for a warning indicator — and verify open-circuit voltage on the outgoing cell reads below 3.4V to confirm depletion.