About this replacement
HP iPAQ RX1900 / RX1950 / RX1955 — 3.7V Li-ion Replacement Battery (PE2018AS)
This is a 3.7V, 2250mAh lithium-ion battery for the HP iPAQ RX1900, RX1950, and RX1955 pocket PCs. It replaces OEM part numbers PE2018AS, 395780-001, HSTNN-H09C-WL, 398687-001, 399858-001, and 35H00063-00M. The cell fits the same bay and connects to the same 3-pin connector as the original HP unit.
- RX1900 / RX1950 / RX1955 platform fit: All three models share the same physical battery bay, connector pinout, and BMS handshake protocol. HP used a single battery spec across this RX series, so one cell covers all three variants without modification.
- Bench tested on actual hardware: We ran this cell on an RX1950 unit and confirmed the BMS initialised correctly on first charge. The protection circuit held within spec at both ends of the charge curve — no false low-voltage cutoff and no overcharge event at full capacity.
- RAM data protection before swap: Perform a full ActiveSync or Windows Mobile Device Center sync to the host PC before removing the battery. The iPAQ RX series holds open application state and contacts in volatile SRAM, which is powered entirely by the main cell. Cut power without syncing and that data is gone.
Why the iPAQ RX1900 loses all data after a battery swap
The RX1900 uses SRAM — static RAM — for its working memory, not flash. SRAM needs continuous power to retain data. The moment the battery is removed, the voltage rail drops and every open file, calendar entry, or app state held in RAM is erased. There is no background flash write on shutdown like a modern smartphone. The only protection is syncing all data to a PC before the cell comes out, then restoring from the sync after the new battery is seated and charged.
iPAQ RX1955 won't boot after new battery installed
The RX1955 boot ROM checks for a minimum supply voltage before it will initialise the processor — if the replacement cell shipped partially discharged, the device may show nothing or loop on the HP splash screen. This is not a fault with the battery or the device. Connect to the OEM charger or a compatible 5V USB source and charge for at least 30 minutes before pressing the power button. If the unit still won't boot after a full charge cycle, hold the reset pin on the base for 10 seconds while connected to power, then retry.