About this replacement
Angel AJ5803 — 12V Ni-MH Replacement Battery (HYHB-762)
This is a 12V, 2000mAh Ni-MH replacement battery for the Angel AJ5803 portable medical device. It replaces OEM part HYHB-762. When the original cell degrades, this restores the voltage rail the AJ5803 needs to complete its startup sequence and sustain normal operation.
- AJ5803 voltage rail match: The AJ5803 BMS expects a 12V Ni-MH charge profile. Substituting a different chemistry or voltage triggers a persistent battery fault because the charge IC and BMS handshake are calibrated to Ni-MH delta-V cutoff behaviour — not lithium charge curves.
- Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence and confirmed the BMS accepted the cell, delta-V cutoff fired at the correct voltage, and the device completed its power-on self-test without a battery fault flag.
- Post-swap startup protocol: After installing this battery, let the AJ5803 run its full power-on self-test without interruption. The BMS runs a chemistry verification check at boot — cutting power mid-sequence causes a false battery fault that persists until the next clean full reboot.
Device not completing boot sequence on new battery
The AJ5803 runs a BMS verification step during boot that checks cell voltage against a minimum threshold. A new Ni-MH cell fresh out of packaging often sits below 11.5V from self-discharge during shipping and storage. If the resting voltage is too low, the device stalls mid-boot or displays a battery error before the screen fully loads. Charge the battery to completion on the OEM or compatible charger before the first installation — confirm charge termination, then reinstall.
Charge indicator not reaching 100% on the first charge cycle
Ni-MH charge ICs use delta-V detection to find peak charge — on a brand-new cell, the voltage rise curve is flatter than a conditioned cell, so some chargers terminate early or report 90–95% instead of full. This is a first-cycle characteristic, not a cell fault. Run one complete charge-discharge-charge cycle to allow the charge IC to calibrate to the cell's actual voltage profile. After that cycle, the charge indicator should reach 100% and hold correctly.