About this replacement
Custom Battery Packs AA20004S1P — 4.8V Ni-MH Replacement Battery Pack
This is a 4.8V 2000mAh Ni-MH replacement battery pack built to the AA20004S1P specification. It runs a four-cell AA configuration in series, delivering 9.6Wh. It fits portable electronics, emergency lighting units, and cordless devices that originally shipped with a four-cell 4.8V Ni-MH pack.
- Four-cell AA series configuration: Four AA Ni-MH cells wired in series produce the 4.8V rail that this pack class requires. Devices spec this configuration because it matches the discharge curve of the original OEM cells — swap one cell count and the voltage rail shifts enough to trigger low-battery cutoff prematurely.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on a cell analyser. The BMS held the 4.8V nominal rail cleanly under steady load, and capacity measured within spec across the first three cycles after an initial conditioning pass.
- First-cycle conditioning on Ni-MH packs: Ni-MH cells ship at storage voltage, not full charge. Run one complete charge-discharge cycle immediately after installation. Devices with integrated fuel gauges will misread state-of-charge until the gauge calibrates against the new cells — one full cycle clears this.
Pack running at lower voltage than rated on first use
Ni-MH cells leave the factory at storage voltage, typically 1.0–1.1V per cell. At four cells in series, that puts the pack at roughly 4.0–4.4V — below the 4.8V nominal rating. The device reads this as a weak or discharged pack, not a fault. Charge the pack fully before first use and the voltage will settle at the rated 4.8V across all four cells.
Pack not reaching full charge on the first cycle
Many charger ICs reduce current on the first charge of a new or long-stored Ni-MH pack — this is the charge controller being cautious with cells it hasn't profiled yet. The pack is not faulty. After the first complete charge cycle, the charge IC adjusts its current delivery and the pack accepts full capacity from cycle two onward. If capacity still reads low after three full cycles, check the charger output is delivering the correct termination voltage of at least 5.5V to the pack terminals.