1/3AA/300X3 Replacement Battery Pack 3.6V 300mAh Ni-MH

Custom Battery Pack 1/3AA/300X3 — 3.6V Ni-MH Replacement Battery

This is a 3.6V 300mAh Ni-MH replacement battery pack built around three 1/3AA cells wired in series. It replaces OEM part number 1/3AA/300X3 in compact electronic devices that originally shipped with this configuration. Typical applications include emergency lighting units, cordless phones, and small portable electronics running on this exact cell format.

• Three-cell series stack: Three 1/3AA cells in series produce the 3.6V rail this device class requires. Any deviation — a mismatched cell, a weak link — shifts the pack voltage outside the charge IC's acceptance window. Every cell in this pack is matched to within 10mV open-circuit before assembly.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the bench. The BMS accepted charge current normally, cell balance held across all three positions, and terminal voltage at end-of-charge measured within spec of the 3.6V nominal rating.
• First-cycle calibration on fuel-gauged devices: If your device has a capacity indicator, run one complete charge-discharge cycle after installation. Fuel gauge ICs track coulombs against a stored baseline — a new cell swap resets that relationship. One full cycle re-anchors the gauge to the actual cell capacity.

Pack running at lower voltage than rated on first use

Ni-MH packs ship at storage voltage, typically 3.2–3.4V across three cells, not the rated 3.6V. Some devices perform a voltage range check on power-up and will report low battery or refuse to operate if the pack reads below their acceptance threshold. This is not a fault with the pack — it is a storage state. Charge the pack fully before first use; terminal voltage will rise to 3.6V and the device should accept it on the next power-on.

Pack not reaching full charge on the first cycle

On the first charge cycle, some charge ICs apply a reduced current to new or long-stored Ni-MH cells, which can make the pack appear to terminate early or report partial capacity. This is a normal conditioning behaviour — the charge controller is reading dV/dT (voltage slope) cautiously on unfamiliar cells. Complete the first charge uninterrupted and follow immediately with a full discharge. The second charge cycle will deliver full capacity as the controller adjusts its termination threshold to the actual cell response.