About this replacement
Sokkia SRX Robotic Total Station — 7.4V Li-ion Replacement Battery (BDC58)
This 7.4V, 4400mAh Li-ion battery replaces the BDC58 and BDC70 packs used in Sokkia SRX robotic total stations and SETX series instruments including the SET230R and SET330R. It delivers the same voltage rail and cell configuration as the original, keeping the instrument's power management system satisfied. Capacity is 32.56Wh — matched to the product data, not estimated from web sources.
- SRX and SETX platform fit: These models share the same battery bay geometry, 7.4V power rail, and BMS handshake protocol. One pack covers the full SRX robotic and SETX conventional lineup, including the SET230R and SET330R, because Sokkia standardised the battery interface across this generation of total stations.
- Bench tested on actual hardware: We ran this pack through a full charge and discharge cycle on an SRX unit. The BMS accepted the handshake without error, reported state-of-charge correctly on the instrument display, and held voltage under sustained servo and EDM load without triggering low-voltage cutoff prematurely.
- Post-install calibration on first field use: After fitting a new pack, run the full instrument calibration sequence through the Sokkia menu before deploying. The total station maps battery state during calibration — skipping this step causes the low-battery indicator to fire early on the first measurement session, even with a fully charged pack.
Why the SRX shuts down at EDM initialisation despite showing a charged battery
When the SRX fires the EDM (electronic distance measurement) module, the instrument draws a sharp current spike to initialise the laser and servo motors simultaneously. An aged original pack with elevated internal resistance can't sustain that spike — voltage sags below the BMS cutoff threshold for a fraction of a second, and the instrument shuts down even though the display showed full charge a moment earlier. This is a cell-level failure, not a software fault. A replacement pack with fresh cells and low internal resistance delivers current fast enough to clear the initialisation spike without triggering BMS cutoff.
Pack shows zero charge and won't power the instrument after months in the carry case
Li-ion cells self-discharge slowly during storage. If the pack drops below approximately 2.5V per cell (5.0V total) while unused in a case, the BMS enters sleep mode and stops responding — the instrument sees no pack at all. Most chargers will also refuse to charge a pack in this state. To recover it, place the pack in the Sokkia CDC68 or compatible charger and leave it connected for at least 30–60 minutes; some chargers include a trickle pre-charge mode that slowly raises cell voltage back above the 3.0V-per-cell recovery threshold before switching to normal charge rate. If the pack doesn't respond after two hours on the charger, the cells have self-discharged past recoverable depth.