About this replacement
Denso SMP-G501 — 3.6V Li-SOCl2 Replacement Battery (410076-0090)
This is a 3.6V 3500mAh lithium-thionyl chloride cell for the Denso SMP-G501 programmable logic controller. It replaces OEM part numbers 410076-0090, 410076-0150, 410076-0180, 410076-0220, 410076-0250, 410076-0260, and LS17500-DST. The cell maintains SRAM program memory and real-time clock data between power cycles.
- SMP-G501 platform compatibility: All listed OEM part numbers reference the same SMP-G501 battery socket — same 3.6V rail, same connector footprint, same BMS handshake threshold. The controller checks nominal voltage at the battery rail; this cell meets that threshold from the first contact.
- Bench tested on actual hardware: We ran this cell against the SMP-G501 battery management circuit. The BMS accepted the cell without fault, voltage settled at 3.6V, and the low-battery alarm cleared. SRAM retention held across simulated power-off cycles with no program data loss.
- Hot-swap procedure for SMP-G501: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off drains SRAM immediately — the program and RTC data are gone the moment the cell is disconnected. If a cold swap happened, a full program reload from the programming device is required.
PLC battery alarm not clearing after confirmed good installation
The SMP-G501 does not auto-clear the battery fault flag when a new cell is fitted. The alarm is latched in firmware and must be reset manually through the programming software — seating the cell alone will not do it. Connect a programming device, navigate to the diagnostics or status register, and clear the battery alarm flag explicitly. Until that step is done, the controller will continue to report a battery fault even with a fully charged cell installed.
New cell reading below 3.6V immediately after installation
Li-SOCl2 cells ship in a passivation state — a thin lithium chloride layer forms on the anode during storage and suppresses initial voltage. On the SMP-G501, this can cause the battery monitor to read 3.2–3.4V for the first few hours. This is not a faulty cell. The float charge from the powered PLC breaks down the passivation layer, and voltage rises to the rated 3.6V within 4–8 hours. Confirm the reading has stabilised at 3.6V before logging the replacement as complete.