Profoto B1 Replacement Battery 14.4V 5000mAh 100323

Profoto B1 / B1X AirTTL Flash Heads — 14.4V Li-ion Replacement Battery (100323 / 100399)

This 14.4V, 5000mAh (72Wh) lithium-ion cell replaces OEM part numbers 100323 and 100399 in the Profoto B1 and B1X AirTTL flash heads. These are battery-powered monolight strobes used for location and studio photography. The battery drives both the capacitor recharge circuit and the head's control electronics between flash cycles.

• B1 and B1X shared battery platform: Both flash heads run the same 14.4V rail and use an identical battery form factor and connector. The BMS on each head communicates charge state to the Profoto Air remote system — the replacement cell uses the same protocol, so remote battery readout functions normally.
• Bench tested on actual hardware: We cycled this cell through repeated full-power capacitor recharges on a B1 head. The BMS held voltage above the low-battery cutoff threshold through sustained burst sequences, and charge state reporting remained consistent across the dock and remote display.
• First-fit power cycle on the B1 and B1X: After inserting a new cell, power the flash head fully off and back on before shooting. The BMS handshake that sets the charge state display initialises from a cold boot — swapping the battery mid-session without a full power cycle can cause the dock or remote to show an incorrect battery level.

Flash output stepping down after 10–15 full-power shots

At full power, the B1's capacitor pulls a high recharge current from the battery in a short window after each flash. If the cell's internal resistance is elevated — common in aged OEM cells — voltage sags during that recharge burst, and the head's protection circuit interprets the drop as low battery and steps the output down. This is not a fault in the head itself. A fresh cell with lower internal resistance sustains the voltage rail through the recharge spike. After fitting this replacement, run five full-power cycles to let the cell's internal resistance settle before judging output consistency.

Dock cycling between charge and ready LED without completing a charge

This symptom appears when the dock's BMS handshake with the battery does not complete cleanly — the dock reads an ambiguous state and toggles between charge and ready rather than committing to either. It happens most often after a battery swap without a full power cycle of the flash head. Remove the battery, leave the dock unplugged for 30 seconds, reinsert the cell, and reconnect the dock to mains. The handshake resets from a clean initialisation state and the charge LED should hold steady.