GP DR35 Replacement Battery 10.8V 5200mAh Li-ion

GP DR35 / DR35S — 10.8V Li-ion Replacement Battery

This 10.8V, 5200mAh (56.16Wh) lithium-ion pack replaces the original battery in the GP DR35 and DR35S survey and measurement instruments. It uses the same voltage rail and connector format as the factory cell. Capacity figure is taken from the product specification, not estimated.

• DR35 and DR35S compatibility: Both models run the same 10.8V bus and share an identical battery bay and BMS handshake protocol. One pack covers both variants — no firmware difference affects charging acceptance on either unit.
• Bench tested on actual hardware: We cycled this pack under a simulated sensor-load profile, including cold-start probe initialisation spikes. The BMS held the output rail steady through each initialisation event without triggering an over-current cutoff.
• First-use calibration on the DR35: After installing this pack, run a full calibration cycle through the instrument menu before going into the field. The DR35 maps battery state during calibration — skipping this step causes premature low-battery warnings during the first measurement session, even when the cell is at full charge.

BMS cutoff when the DR35 probe module initialises

When the DR35 powers up a connected probe, the sensor draws a short inrush current that can exceed the BMS over-current threshold on a degraded or deeply discharged pack. The BMS interprets this spike as a fault and cuts output before the probe finishes initialising. This replacement pack carries a higher cell capacity, which lowers internal resistance and reduces the voltage sag during that inrush event. If the instrument still cuts out at probe start, check that the cell is above 10.0V before powering the probe module.

DR35 not recognising the new pack after it sat unused in storage

A lithium-ion cell that has been stored discharged for several months can drop below the BMS recovery threshold — typically around 2.5V per cell, or roughly 7.5V for a 3S pack. When cell voltage sits that low, the BMS enters sleep mode and the instrument sees no communication from the pack at all. Place the battery on a compatible charger and allow a slow pre-charge cycle to bring each cell back above 3.0V. Once the BMS exits sleep mode and the pack reads above 9.5V total, the DR35 will recognise it normally.