JCB Toughphone Sitemaster 2 Compatible Battery 3.7V 1450mAh

JCB Toughphone Sitemaster 2 / TP305 — 3.7V Li-ion Replacement Battery

This is a 3.7V Li-ion replacement battery rated at 1450mAh (5.37Wh) for the JCB Toughphone Sitemaster 2 and TP305. Both models share the same battery bay dimensions (56.00 x 34.10 x 7.70mm) and the same cell voltage rail. It replaces a worn or failed original cell to restore normal phone operation on site.

• Sitemaster 2 and TP305 fitment: These two models use the same battery footprint, connector pinout, and BMS communication protocol — one cell fits both. No modification needed at the housing or contact plate.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Sitemaster 2 platform. The BMS handshake completed correctly on first insertion, and the charge IC accepted the cell without fault codes or thermal cutoff events.
• Fuel gauge recalibration on first use: On first use after fitting, disable fast charging and run one full discharge-to-charge cycle. The phone's fuel gauge IC calibrates to the new cell's discharge curve during this cycle. Skipping it can cause the percentage readout to jump or report cutoff at the wrong level.

Sudden shutdown at 20–30% on the Sitemaster 2

This happens when the fuel gauge IC still holds the discharge curve of the old, degraded cell. The phone thinks 20% is a safe level, but the new cell's actual voltage under modem and screen load drops sharply at that point. The voltage cliff triggers the protection circuit before the OS can execute a clean shutdown. One full discharge-to-charge cycle with fast charging off resets the coulomb counter and maps the new curve correctly — after that, the percentage reading tracks accurately.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge in storage. If this cell sat long enough to drop below approximately 2.5V, the BMS enters lockout mode and blocks charge input as a protection measure. The phone will show no response — no charging indicator, no boot. Connect the phone to a wall charger rated at least 5V/1A and leave it for 20–30 minutes without pressing anything. The charge IC applies a trickle current that slowly brings the cell above the BMS recovery threshold, after which normal charging resumes.