About this replacement
SAT-KABEL SPM 22 / IRM Series — 6V Ni-MH Replacement Battery (35512A)
This is a 6V 700mAh Ni-MH battery built to the 35512A specification. It fits the SAT-KABEL SPM 22 surveying instrument along with the IRM 5, IRM 7, and IRM 70. All four instruments share the same battery bay geometry, connector pin-out, and charge-control interface.
- SPM 22, IRM 5, IRM 7, IRM 70 compatibility: These instruments run from the same 6V regulated rail and use an identical mechanical housing with a common connector. The charge termination logic — delta-V detection at the instrument side — is the same across all four, so one cell pack handles the full range without modification.
- Bench tested on actual hardware: We cycled this pack through the SPM 22 charge and discharge sequence. The BMS held cutoff voltage cleanly at 5.5V under sustained sensor load, and delta-V termination triggered correctly at full charge with no overrun into trickle-only territory.
- First-use calibration on the SPM 22: After fitting a new pack, run a full calibration cycle through the instrument menu before taking it to site. The SPM 22 maps battery state during calibration — skipping this step causes the low-battery indicator to fire early on the first measurement session, even when the pack is fully charged.
Why the SPM 22 shuts down at probe initialisation
When the SPM 22 powers up a connected probe or sensor module, it pulls a short current spike — often 400–600mA — in the first 200ms. An aged or deeply discharged Ni-MH pack cannot hold voltage through that spike, and the instrument's under-voltage lockout trips before the main measurement session even starts. A new 700mAh pack with low internal resistance handles the initialisation draw without a voltage dip large enough to trigger cutoff. If the unit still shuts down at startup after fitting a new pack, check that the battery contacts in the bay are clean and making full surface contact.
Pack will not charge after the instrument sat unused for months
Ni-MH cells self-discharge steadily in storage — a pack left in a carry case for several months can drop below 4.8V total, which sits under the threshold the SPM 22 charger circuit recognises as a valid pack. The charger sees the low voltage and refuses to initiate a charge cycle. To recover the pack, connect it to an external Ni-MH charger with a force-charge or recovery mode, which applies a low-rate trickle at around 70mA to bring cell voltage back above 1.0V per cell before the main charge begins. Once the pack reads above 5.4V, the instrument's own charger will accept it normally.