Sena Spider ST1 Replacement Battery 3.7V 800mAh AHB802540

Sena Spider ST1 / SP105 / SP88 — 3.7V Li-Polymer Replacement Battery (AHB802540)

This is a 3.7V, 800mAh Li-Polymer replacement cell for the Sena Spider ST1 Bluetooth motorcycle headset and its SP105, SP88, and Spyder 1S siblings. All four models share the same AHB802540 cell and connector. The pack sits inside the helmet-mount unit and powers the combined Bluetooth radio, audio output, and microphone circuit.

• Spider ST1, SP105, SP88, Spyder 1S fit: These headsets share the same 3.7V power rail, physical cell footprint (42.60 × 24.70 × 7.80mm), and BMS handshake protocol — so a single cell covers the full range. No wiring modifications needed.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the Spider ST1 unit. The BMS accepted the cell without fault codes, and the protection circuit tripped correctly at low-voltage threshold as expected.
• First-cycle charging on the Spider ST1: Place the headset in its cradle and run one full charge before making any calls. The ST1's talk-time indicator pulls its estimate from the BMS log — a new cell starts at storage voltage, so the display will read inaccurate until the first complete cycle finishes.

Talk time shorter than rated on the first few charges

Li-Polymer cells ship at storage voltage — roughly 3.6V — not at full capacity. The Spider ST1 draws from the Bluetooth radio, audio amplifier, and microphone simultaneously, so any shortfall in initial cell voltage shows up quickly under combined load. Talk time typically improves across three to five full charge-discharge cycles as the cell reaches its rated 800mAh capacity. If talk time is still noticeably short after five cycles, check that the cradle contacts are clean and making solid contact with the headset terminals.

Headset cutting out mid-call on a new battery

Mid-call dropout on a freshly fitted cell is almost always a voltage sag event. The Spider ST1 peaks its draw when Bluetooth transmission and audio output fire at the same moment — if the cell hasn't completed its first full cycle, that instantaneous load can drag voltage below the BMS cutoff threshold. The headset powers off to protect the cell. The fix is straightforward: complete two or three full charge cycles before extended use, and confirm the replacement cell matches the 3.7V nominal voltage exactly — a mismatched cell will sag harder under peak draw.