TerraMow S800 Replacement Battery 21.6V 6700mAh C1276A8

TerraMow S800 / S1200 — 21.6V Li-ion Replacement Battery (C1276A8)

This is a 21.6V lithium-ion replacement battery rated at 6700mAh (144.72Wh), built to the C1276A8 specification. It fits the TerraMow S800 and S1200 cordless lawn mowers. Swap it when your original pack no longer holds a charge or grab a second one to keep mowing without waiting on a recharge.

• S800 and S1200 compatibility: Both models run the same 21.6V power rail, use the same battery connector, and communicate with the same BMS handshake protocol — which is why a single C1276A8 pack covers both platforms without any modification.
• Bench tested on actual hardware: We ran this pack through full charge-discharge cycles on an S800 deck, including a simulated heavy-grass load sequence. The BMS managed cell balancing correctly and held cutoff voltage within spec across all test cycles.
• Seasonal storage tip: Before your first mow of spring, bring the battery indoors overnight if temperatures are below 10°C. Cold Li-ion cells carry higher internal resistance, and the blade motor's inrush current can trip the BMS on a cold pack before the mower even starts cutting.

BMS cutoff on thick-grass and wet-grass blade load

The S800 blade motor draws significantly more current when cutting thick or wet grass. If that inrush current exceeds the BMS protection threshold — even briefly — the pack shuts down as a safeguard against cell damage. This is not a battery fault; it is the protection circuit doing its job. Reduce the cutting width or raise the deck height when conditions are heavy, and the BMS will stay within its operating window.

Charger showing a fault light after the mower sat unused all winter

Lithium-ion cells self-discharge slowly during storage. If the pack sat below roughly 2.5V per cell over winter, the charger's acceptance circuit will reject it and show a fault. Place the battery in a warm room (above 15°C) for two hours, then reconnect it to the charger. Most chargers will then enter a slow pre-charge mode and recover the pack — if the fault light clears within 30 minutes, the recovery is working.