Graphtec GL220 Data Logger Replacement Battery 7.4V 2200mAh

Graphtec GL220 Data Logger — 7.4V Li-ion Replacement Battery (B-517)

This 7.4V 2200mAh Li-ion battery replaces the Graphtec B-517 in the GL220 data logger. The GL220 is a portable field instrument used to record temperature, humidity, and environmental data where mains power is unavailable. Same voltage, same capacity, same connector footprint as the original cell.

• GL220 compatibility: The GL220 uses a dedicated Li-ion pack at 7.4V nominal — the BMS inside the logger handshakes with the cell to regulate charge cutoff and discharge floor. This replacement matches that voltage rail and the physical connector orientation so the logger recognises the pack without throwing a battery fault.
• Bench tested on actual hardware: We cycled this cell through the GL220's charge circuit and confirmed the BMS accepted the pack, reached full charge without error flags, and held voltage steady across the discharge curve under continuous logging load.
• Field deployment tip: Before taking the GL220 out for a long monitoring run, complete one full charge cycle and start a short test recording session. This lets the logger's BMS establish accurate state-of-charge tracking on the new cell — skipping this step can cause the battery indicator to read incorrectly in the first few sessions.

Why the GL220 shows a low battery warning with a new cell installed

The GL220 estimates remaining charge using a coulomb-counting algorithm that builds its baseline during the first full charge-discharge cycle. A brand-new cell installed mid-session gives the logger no reference point, so the state-of-charge estimate starts from wherever the previous pack left off. This causes the battery indicator to show low or erratic readings even when the new cell is at full voltage. Run one complete charge from flat to 8.4V and let the logger complete a discharge cycle to reset the counter correctly.

GL220 powers off mid-recording session unexpectedly

The GL220's BMS enforces a hard undervoltage cutoff — typically around 6.0V — to protect the cell from deep discharge damage. An aged or partially discharged battery reaches this floor faster than expected, and the logger shuts down instantly without a warning log entry. If the unit powers off mid-session and restarts normally on AC, the cell voltage dropped below the cutoff threshold rather than a firmware fault. Charge the pack fully to 8.4V before the next deployment and check that the voltage reads above 7.2V at the start of the session.