Philips SBOQBOX 7.4V Replacement Battery 3400mAh Li-ion

Philips ShoqBox SB500M Series — 7.4V Li-ion Replacement Battery (INR18650-2S)

This is a 7.4V, 3400mAh (25.16Wh) Li-ion battery for the Philips SBOQBOX and SB500M portable speaker range. It fits the SB500M, SB500M/00, and ShoqBox SB500M. When the original cell degrades after repeated cycles, audio output weakens and charge retention drops — this battery restores full pack capacity.

• SB500M series fitment: The SBOQBOX, SB500M, and SB500M/00 all share the same 7.4V two-cell Li-ion pack with identical connector pinout and BMS communication protocol. Swapping to this battery requires no modifications — the speaker's charge controller recognises the cell chemistry and initiates a standard CC/CV charge cycle.
• Bench tested on actual hardware: We cycled this battery through full charge and discharge passes on the SB500M platform. The BMS held cutoff at the correct lower voltage threshold and did not trigger premature protection trips during sustained audio playback at high amplifier draw.
• Monthly full-discharge cycle for ShoqBox users: Let the speaker run below 20% charge at least once a month before plugging it back in. Constantly topping off the pack at 80–90% without a deeper discharge causes fuel gauge drift — the speaker reports more charge than the cells actually hold, and audible performance drops sooner than expected.

Voltage sag under combined amplifier and Bluetooth radio draw at high volume

At high volume the SB500M's amplifier and Bluetooth radio pull current simultaneously. A degraded or partially charged cell cannot sustain voltage under that combined load and sags below the amplifier's minimum rail. The BMS reads this as a fault condition and either throttles output or cuts power briefly. A fresh cell at full charge holds the voltage rail stable through those high-draw peaks without triggering the protection circuit.

Speaker shows full charge indicator but audio clips and distorts before the battery reads empty

This is amplifier clipping caused by voltage sag, not a firmware or speaker fault. When cell capacity has faded, internal resistance rises — the pack can report a healthy state of charge but cannot deliver enough current under load. The amplifier hits its minimum supply voltage and clips the audio signal before the fuel gauge reaches the low-battery threshold. Charge the new battery to 100% and run a full discharge cycle to recalibrate the fuel gauge to the cell's actual capacity.