Energizer ER-GUM1 Replacement Battery 1.2V 1200mAh Ni-MH

Energizer ER-GUM1 — 1.2V Ni-MH 1200mAh Replacement Battery

This is a 1.2V, 1200mAh Ni-MH replacement battery for the Energizer ER-GUM1. It fits portable media players that use this cell format. Capacity matches the original at 1200mAh (1.44Wh).

• ER-GUM1 cell format: Media players using this slim cell run a 1.2V rail with tight physical constraints — 66.78 x 16.70 x 5.96mm. Any deviation in cell dimensions blocks the battery door or breaks contact alignment. This cell matches that envelope exactly.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a compatible media player. The BMS accepted charge current without interruption and held voltage through full playback cycles without unexpected cutoff.
• Post-storage charge protocol: If the player has sat unused for several months, connect it to the charger for at least 30 minutes before attempting to power it on. Media players using Ni-MH cells can enter a deep-discharge protection state that blocks normal startup until the cell recovers a minimum voltage threshold.

Playback cutting out before the battery indicator hits empty

Ni-MH cells discharge with a relatively flat voltage curve that drops sharply near the end of capacity. Audio amplifier circuits draw a spike of current on each output cycle, and that spike can pull cell voltage below the device's cutoff threshold before the fuel gauge registers empty. The result is abrupt playback shutdown while the indicator still shows charge remaining. A full conditioning cycle — charge to 100%, discharge fully, then recharge — helps the device recalibrate its voltage thresholds to the new cell. After conditioning, the cutoff point should align more closely with the indicator.

Battery percentage jumping erratically after cell swap

Media players estimate remaining charge by tracking voltage against a stored discharge curve. After installing a new cell, the device's internal model is mismatched to the fresh cell's actual voltage profile. This causes the percentage indicator to jump — often from 80% straight to 20%, or vice versa — during the first few charge and discharge cycles. Run two to three full charge-discharge cycles without interruption. The indicator stabilises as the device maps measured voltage back to its stored capacity model.