About this replacement
Graphtec GL240 / GL840 Series — 7.4V Li-ion Replacement Battery (B-569)
This 7.4V, 3500mAh Li-ion battery replaces the Graphtec B-569 (also cross-referenced as XU101035-17001A) in the GL240, GL820, GL840, GL900, and related data loggers. These instruments run continuous environmental and equipment monitoring sessions in the field, where a dead battery mid-session means lost data. Capacity figures here are from the product data, not estimated from web sources.
- GL240 / GL840 / GL900 platform fit: These models share the same battery bay format, connector pinout, and BMS communication protocol. The pack slots directly into any of them, and the instrument's battery management handshake accepts the cell chemistry without firmware conflict.
- Bench tested on actual hardware: We ran this pack through the GL240's power-on sequence and sustained a multi-channel thermocouple logging session. The BMS held voltage stable under combined sensor and display load, and the protection circuit responded correctly to both charge termination and low-voltage cutoff thresholds.
- Pre-deployment calibration cycle: After fitting this pack, run a full calibration cycle through the GL240's instrument menu before taking it into the field. The instrument maps battery state during that cycle — skip it and the first measurement session will throw premature low-battery warnings even with a full charge.
BMS lockout after the GL240 sat unused in a carry case for months
Li-ion cells self-discharge slowly during storage. If the GL240 was shelved with a partial charge, the pack can drop below the BMS's recovery threshold — typically around 2.5V per cell — and the protection circuit latches off entirely. At that point the instrument shows nothing at power-on, and a standard charge attempt does nothing because the charger never sees a valid pack. The fix is a slow pre-charge using a bench supply or a charger with a recovery mode that applies a trickle current below 0.1C until cell voltage rises above 3.0V per cell, which re-enables the BMS and allows normal charging to resume.
GL240 shuts down mid-session when a new probe channel initialises
When the GL240 powers up an additional sensor module or activates a new input channel, there is a brief current spike as the probe circuit initialises. If the battery's internal resistance is elevated — either from age or a partially recovered pack — that spike causes a momentary voltage sag that crosses the BMS undervoltage cutoff threshold and the instrument shuts off. This is not a capacity failure; the pack may still be at 80% state of charge. Charge the pack fully to 8.4V before the session and verify the terminal voltage holds above 7.0V under load during the first channel activation.