About this replacement
NiKon DTM-302 / NPL-302 Series — 7.2V Ni-MH Replacement Battery (4/UR17650/3500)
This is a 7.2V, 3500mAh Ni-MH replacement battery for the NiKon DTM-302 and NPL-302 total station series, including the DTM-350 and NPL-350. It slots into the battery compartment on the instrument body and powers the angle encoder, EDM module, and display. Capacity matches the original pack at 3500mAh (25.2Wh).
- DTM-302 / NPL-302 / DTM-350 / NPL-350 compatibility: These instruments share the same battery bay geometry, 7.2V voltage rail, and contact arrangement. The BMS handshake on each model reads cell voltage directly — no proprietary authentication chip — so a correctly rated Ni-MH pack is accepted without firmware rejection.
- Bench tested on actual hardware: We cycled this pack through simulated EDM and angle-encoder load sequences. The BMS held stable under the initialisation current spike at power-up and did not trip during sustained measurement logging.
- Post-install calibration cycle: After fitting a new pack, run a full calibration sequence through the instrument menu before field deployment. The DTM-302 maps battery state during that cycle — skip it and the low-battery indicator will fire early on the first session, even with a fully charged pack.
BMS lockout after the DTM-302 sat unused in a carry case for months
Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A pack stored in a case over a long field off-season can drop below the BMS recovery threshold — typically around 5.4V for a 7.2V pack — and the protection circuit opens, blocking both charge and discharge. The charger shows no activity and the instrument does not power on. To recover, connect to the OEM charger (BC-60 or BC-65) and leave it for 20–30 minutes; most BMS circuits will accept a trickle pre-charge pulse that brings cells back above the recovery threshold before switching to full charge.
DTM-302 shuts down mid-measurement with no prior low-battery warning
This happens when cell voltage sags sharply under the combined draw of the EDM ranging pulse and the angle encoder — a load the instrument cannot sustain if any cells in the pack have developed high internal resistance from age or deep discharge. The BMS reads the sag as an under-voltage fault and cuts the circuit instantly, without triggering the low-battery display first. A fresh pack at full charge will hold voltage above the cutoff threshold through that combined load. If the new pack still shuts down, check that the battery contacts on the instrument are clean — oxidised contacts add resistance and can push the voltage reading below the BMS threshold even with a healthy pack.