About this replacement
CriticalResponse M1501 / REH-1501 — 3.7V Li-ion Replacement Battery (CS523450AL 1S1P)
This is a 3.7V, 1050mAh Li-ion cell for the CriticalResponse M1501 and REH-1501 pagers. It matches the OEM part number CS523450AL 1S1P and fits the same physical footprint at 53.40 × 38.00 × 7.50mm. These pagers are used in healthcare, emergency services, and industrial environments where alert delivery cannot be interrupted.
- M1501 and REH-1501 compatibility: Both models use the same single-cell Li-ion holder, voltage rail, and contact arrangement. One cell covers both — no wiring or adapter needed.
- Bench tested on actual hardware: We ran this cell through charge acceptance and BMS handshake verification. The protection circuit responded correctly to both low-voltage cutoff and over-charge thresholds at 3.7V nominal.
- Post-swap power cycle: After fitting the new cell, power the pager fully off and back on. Some M1501 units require a fresh boot to re-register on the paging network and reset the low-battery indicator to the new voltage baseline.
Why the M1501 drains faster during high-traffic alert periods
The M1501 draws more current when it receives frequent pages or when the signal from the local transmitter is weak and the receiver has to work harder. A 1050mAh cell at 3.7V has a fixed energy budget of 3.89Wh. Heavy alert traffic and extended signal-search cycles both pull from that budget faster than light-use standby. If your environment has changed — new building, relocated transmitter, increased message volume — expect shorter intervals between charges.
Low battery warning appears immediately after fitting a new cell
Cells ship at storage voltage, typically around 3.6–3.65V, which sits below the M1501's low-battery threshold. The pager sees this and flags the warning before the cell has been used at all. Charge the pager normally for a full cycle — once the cell reaches its working voltage range above 3.7V, the indicator clears. No fault with the cell or the device.