Kalkhoff Agattu C3 Nexus Compatible Battery 25.2V 18000mAh

Kalkhoff Agattu C3 Nexus — 25.2V Li-ion Replacement Battery

This 25.2V, 18000mAh (453.6Wh) lithium-ion battery replaces the original pack on the Kalkhoff Agattu C3 Nexus (2012) and related Agattu models. It fits across the 2012–2013 Agattu range where the same 25.2V rail and connector format is shared. Use the Fit Model list to confirm your frame year before ordering.

• Agattu 2012–2013 platform fit: The Agattu C3, C7, C8 26, and P7 26 Nexus models share the same 25.2V battery rail and physical mounting slot. The BMS handshake protocol is consistent across this range, so one pack covers the full group without modification.
• Bench tested on actual hardware: We cycled this pack under sustained motor load and monitored BMS response at peak draw. Cell balancing remained stable across full discharge, and the BMS did not trip on simulated hill-climbing current spikes.
• Post-storage charge protocol: After winter storage, run the first charge slowly — Li-ion cells stored below 10°C develop elevated internal resistance. Fast charging cold cells causes lithium plating on the anode, which permanently reduces total cycle life. Let the pack reach room temperature before connecting the charger.

BMS cutoff under sustained climbing load on the Agattu motor

The Agattu's mid-drive system draws sustained high current on extended inclines — more than short flat-ground bursts. If the BMS detects cell voltage dropping below its low-cell threshold during that sustained draw, it trips the output to protect the cells. A degraded original battery trips sooner because its internal resistance is higher, making voltage sag worse under load. A fresh pack with lower internal resistance holds cell voltage above the BMS trip point longer, which is why replacing the battery resolves cutouts that have nothing to do with the motor itself.

Charger LED stays green or won't initiate charge after the pack has been sitting unused

When a Li-ion pack self-discharges below roughly 2.5V per cell during storage, most chargers read it as a fault or an absent pack and refuse to start a charge cycle. This is not a charger fault — it is a cell voltage floor protection response. Connect the charger and leave it plugged in for 30 minutes without interruption; many chargers include a recovery mode that trickle-feeds current until cells reach the acceptance threshold of around 3.0V per cell. If the charger still shows no activity after 30 minutes, the pack has likely dropped below recoverable voltage.