About this replacement
Canon BJ-I70 / BJ-I80 / Pixma I70 Series — 10.8V Li-ion Replacement Battery (LB-51)
This 10.8V, 3400mAh lithium-ion battery replaces the Canon LB-51 (also sold as 0074B001, LK-51B, LB-50, 8409A002, LK-51, K30204) in the BJ-I70, BJ-I80, BJ-IP90, and Pixma I70 series portable inkjet printers. It restores cordless print capability when the original cell has degraded or failed. Capacity matches Canon's original 36.72Wh specification.
- BJ-I70 / BJ-I80 / BJ-IP90 compatibility: These models share the same 10.8V three-cell pack architecture, the same LB-51 connector pinout, and the same BMS handshake protocol — which is why a single replacement covers the full range. Swapping cells without matching the BMS communication would cause the printer to reject the pack entirely.
- Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on a BJ-I70 unit and monitored BMS communication at the connector. The protection circuit responded correctly to both the printer's charge request and its low-voltage cutoff threshold — no false rejections logged.
- First print cycle prep: Charge the battery to 100% before the first print run. The motor drive and heating element together draw peak current at startup — a partially charged cell can trip the BMS on the very first cycle and leave the printer unresponsive until the pack is reset via a full charge.
Why the BJ-I70 stops printing mid-job even with charge remaining
The BJ-I70's heating element and paper feed motor fire simultaneously during each print pass. That combined draw spikes current well above idle levels and can pull cell voltage below the BMS cutoff threshold — even when the indicator shows 30–40% remaining. An aged or deeply cycled cell has higher internal resistance, so the voltage sag under load is more severe than a fresh cell at the same state of charge. The printer interprets the voltage dip as a depleted pack and halts. A replacement cell with lower internal resistance eliminates the sag and keeps voltage above the cutoff during peak draw.
Printer shows "battery full" but won't start a print job
This happens when the BMS has entered a locked state after a deep discharge — the fuel gauge reads correctly but the protection circuit blocks output current. The printer receives the state-of-charge signal but the BMS will not release the discharge FET. To reset it, connect the battery to the printer with the AC adapter plugged in and leave it charging for a full cycle without interrupting. If the BMS does not re-initialise after one complete charge to 10.8V, the cell itself has reached end of life and replacement is the next step.