Blaupunkt BT Drive Free 111 Replacement Battery 3.7V 900mAh

Blaupunkt BT Drive Free 111 — 3.7V Li-ion Replacement Battery (TM533443 1S1P)

This is a 3.7V, 900mAh Li-ion replacement cell for the Blaupunkt BT Drive Free 111 portable car speaker. It also fits the BT Drive Free 112, 211, and 311 — all four models share the same battery footprint and connector. Dimensions are 46.20 × 34.14 × 5.68mm, matching the original cell exactly.

• BT Drive Free 111 / 112 / 211 / 311 platform: These four models run the same internal amplifier board and draw from an identical 3.7V single-cell configuration. The BMS handshake, connector pinout, and physical envelope are consistent across all four, so one cell covers the full range.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the BT Drive Free platform. The BMS accepted charge without fault and held the protection cutoff at the correct low-voltage threshold — no false trips at normal listening levels.
• First-cycle volume tip: Run the speaker at 60% volume during the first charge cycle. Sub-bass frequencies pull peak current from a fresh cell before it is conditioned. Driving the amplifier hard on cycle one can trigger BMS protection prematurely and shorten early capacity.

Bass losing depth at high volume on the BT Drive Free 111

Sub-bass frequencies — typically 60Hz and below — draw short, high-current spikes from the cell. On a degraded or partially discharged battery, those spikes cause the terminal voltage to sag below what the amplifier needs to sustain full output. The result is bass notes that sound thin or drop out entirely while mid and high frequencies remain clear. This is a voltage-sag symptom, not a speaker fault — a fresh cell at full charge resolves it.

Speaker distorting before the battery indicator shows low

The BT Drive Free 111 reads battery level from a resting voltage sample, not under load. As the cell ages, its internal resistance rises — voltage drops sharply when the amplifier draws current, but recovers the moment demand drops. The fuel gauge sees the recovered voltage and reports a healthy charge while the amplifier is already clipping under load. If you hear distortion at moderate volume but the indicator still shows two or three bars, internal resistance is the cause. Replacing the cell restores the load voltage the amplifier needs to operate cleanly.