SpectraLink BPX100 Replacement Battery 3.6V 1100mAh Ni-MH

SpectraLink BPX100 / I640 Series — 3.6V Ni-MH Replacement Battery (SK37H1-D)

This is a 3.6V, 1100mAh Ni-MH replacement battery for the SpectraLink BPX100 cordless handset and related models in the I640, PTX110, and PTX151 lines. It slots into the handset and restores wireless voice capability when the original pack no longer holds a usable charge. Capacity is 3.96Wh, matching the original specification.

• BPX100, I640, PTX110, PTX151 compatibility: These handsets share the same 3.6V single-cell NiMH bay, connector pinout, and base-station charge circuit. The SK37H1-D pack fits all of them without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a BPX100 handset. The BMS accepted charge immediately from a cold state, and voltage held steady under simulated RF transmit load without triggering a low-voltage cutoff.
• First-charge conditioning for NiMH handsets: Place the handset in the base cradle for a full 16-hour charge before first use. NiMH cells in cordless phones need a slow initial charge to reach rated capacity — skipping this step is the single most common cause of short talk time on new replacement packs.

Why range drops on the BPX100 after a battery swap

The BPX100 transmitter draws a sharp current spike each time it sends a DECT burst. If the NiMH pack is not fully conditioned, internal resistance is higher than rated, and voltage sags during that spike. The base station interprets the weak signal as distance — not a battery issue — so the handset shows full bars but range is reduced. After three to five full charge cycles, internal resistance drops and the voltage sag shrinks. If range is still short after five cycles, check that the handset is seating fully in the cradle and the charge contacts are clean.

Base station shows no-charge or error light after installing new pack

NiMH packs lose voltage during storage and can arrive below the threshold the SpectraLink base station uses to detect a valid battery — typically around 3.0V. When the base sees a voltage below that threshold, it flags an error instead of starting a charge cycle. Remove the handset, leave it out of the base for 30 seconds, then reseat it firmly so all three charge contacts are touching. If the error persists, check that the pack voltage reads at least 2.8V with a multimeter — anything below that may need a manual trickle-charge pulse before the base will accept it.