JBL Play Up Replacement Battery 3.7V 1350mAh Li-ion

JBL Play Up / MD-51W — 3.7V Li-ion Replacement Battery (TM533855 1S1P)

This is a 3.7V, 1350mAh (5Wh) Li-ion replacement battery for the JBL Play Up and MD-51W portable Bluetooth speaker. It slots into the same physical footprint as the original cell at 60.12 × 38.12 × 5.75mm. When the original pack can no longer hold a charge, this cell restores wireless audio playback.

• Play Up and MD-51W compatibility: Both the Play Up and MD-51W run on the same single-cell 3.7V rail with the TM533855 1S1P pack configuration. The BMS pinout and physical connector are shared across this speaker variant, so the same cell serves both model designations without modification.
• Bench tested on actual hardware: We cycled this cell through repeated charge and discharge passes on the Play Up chassis. The onboard BMS accepted the cell without fault codes, voltage settled at 4.19V fully charged, and protection cutoff triggered correctly at the low-voltage threshold.
• Li-ion cycle health for daily-use speakers: If the Play Up sits on a desk and gets topped off repeatedly without ever dropping below 50%, the fuel gauge drifts over time and reported capacity shrinks faster than actual cell wear. Let the battery drop below 20% at least once a month before recharging to keep the gauge calibrated.

Why the Play Up audio cuts in and out at high volume on a new battery

At high volume the amplifier and Bluetooth radio draw current simultaneously, creating a combined spike the single 1350mAh cell has to meet in a very short window. If the cell has any internal resistance — from age, a partial charge, or a cold environment — the terminal voltage sags momentarily under that combined load. The speaker's protection circuit reads the sag as a low-voltage event and interrupts audio output before the battery indicator moves at all. Warming the speaker to room temperature and ensuring the cell is charged above 3.8V before a high-volume session reduces the frequency of these interruptions.

Play Up won't wake from USB charging after sitting unused for weeks

A single Li-ion cell left in storage self-discharges slowly, and if the terminal voltage drops below roughly 2.5V, the BMS locks the pack into deep-discharge protection mode. When that happens, plugging in a standard USB charger produces no response — the charger handshake requires the cell to present a minimum acceptance voltage that a locked pack cannot provide. The fix is to connect the speaker to a USB power source and leave it undisturbed for 20 to 30 minutes without pressing any buttons; most BMS circuits on this pack will trickle-charge the cell back above the acceptance threshold and then switch to normal charge mode. If the charge LED still does not illuminate after that window, check that the USB cable is data-capable and supplying at least 5V 1A.