About this replacement
Kyocera Hydro XTRM / C6721 / C6522 — 3.7V Li-ion Replacement Battery (SCP-52LBPS)
This is a 3.7V, 1450mAh Li-ion replacement battery for the Kyocera Hydro XTRM, C6721, C6522, and C6522N smartphones. OEM part numbers SCP-52LBPS and 5AAXBT059GEA confirm fitment across all four variants. Install it when the original cell no longer holds a usable charge or fails to power the device.
- Hydro XTRM / C6721 / C6522 compatibility: All four models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The same cell services the full platform without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the C6721 platform. The BMS accepted the handshake without fault codes, and the charge IC ramped current normally through CC and CV phases.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one full discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell — preventing erratic percentage readings from the first day.
Sudden shutdown at 20–30% on the Hydro XTRM after a cell swap
This is a voltage cliff problem, not a capacity problem. The Hydro XTRM's modem and display draw a combined surge load that causes a worn or freshly installed cell to sag below the BMS cutoff threshold — typically around 3.2V — even while the fuel gauge still reads 20–30%. The phone shuts down because the battery voltage dropped under load, not because the reported percentage was accurate. One full calibration cycle corrects the fuel gauge IC's reference curve and eliminates most of these early cutoffs.
Phone warm near the battery compartment on the first charge after replacement
A new cell starts with higher internal impedance than a cell that has been cycled. The charge IC on the Hydro XTRM applies a constant-current phase that generates more heat against that higher impedance during the first one or two charges. This is normal and reduces after the initial cycles lower the cell's impedance. If the phone stays warm beyond the second full charge, check that the battery contacts are seated flat — a misaligned contact increases resistance and sustains the heating.