About this replacement
Bullard PA20 Air Purifying System — 4.8V Ni-MH Replacement Battery (PA1RBAT)
This 4.8V Ni-MH battery replaces the OEM pack in the Bullard PA20 Air Purifying System, a powered air-purifying respirator (PAPR) used in healthcare and industrial respiratory protection. It fits both the PA20 Air Purifying System and PA20 Respirator variants. Capacity is 3800mAh (18.24Wh), matching the original power spec.
- PA20 platform fit: Both listed PA20 variants share the same battery bay dimensions, connector pinout, and 4.8V voltage rail. The BMS in each unit reads cell chemistry the same way, so this pack communicates correctly with the charge management circuit in both configurations.
- Bench tested on actual hardware: We cycled this pack through the PA20's charge sequence and monitored BMS handshake throughout. The protection circuit flagged no faults, current draw held steady across the load profile, and the cell temperature stayed within spec at full draw.
- Post-installation self-test protocol: After fitting this battery, allow the PA20 to complete its full power-on self-test without interrupting the sequence. The device BMS runs a verification check at startup — cutting power mid-cycle can register a false battery fault that persists until the next complete reboot.
PA20 Low Battery Alarm Triggering on a Fully Charged Replacement Pack
The PA20's BMS uses stored discharge curve data calibrated to an aged OEM cell. A new Ni-MH pack presents a slightly different internal resistance profile, which the charge IC interprets conservatively. The alarm threshold check compares voltage under load — a new cell can momentarily sag below that threshold on the first one or two cycles before the BMS recalibrates. Run one complete charge and discharge cycle before drawing conclusions about battery state. After that cycle, the alarm behaviour should normalise.
PA20 Refusing to Power On After Replacement Battery Sat in Storage
Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A pack stored for several months can drop below the PA20's BMS recovery threshold — typically around 4.0V for a 4.8V nominal pack — causing the unit to refuse to boot entirely. Place the battery on charge before installing it into the device. Most chargers will trickle-charge a deeply discharged Ni-MH cell back above the recovery floor; once voltage climbs above approximately 4.2V, the PA20 BMS will accept the pack and allow a normal startup.