Tevion MD6400 Compatible Battery 3.7V 680mAh Li-ion

Tevion MD6400 / MD7300 — 3.7V Li-ion Replacement Battery (119443)

This is a 3.7V, 680mAh (2.52Wh) lithium-ion replacement battery for the Tevion MD6400 and MD7300 smartphones. It slots directly into either model using OEM part number 119443 and connects via the original battery connector. Replace it when the existing cell holds insufficient charge or will not power the phone through normal use.

• MD6400 and MD7300 compatibility: Both models share the same 3.7V single-cell architecture, connector pinout, and BMS handshake protocol — which is why one cell covers both. The 53.04 × 40.03 × 4.10mm footprint matches the battery bay on either device without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench and confirmed the BMS communicates state-of-charge correctly to the fuel gauge IC. Charge acceptance was stable from 0% to 100% with no cutoff anomalies detected.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one full discharge-to-charge cycle before enabling it again. This allows the fuel gauge IC to recalibrate its coulomb counter against the new cell's discharge curve — skipping this step causes erratic percentage readings in the first few days.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC is still using the discharge curve from the old, degraded cell. The new cell hits a steeper voltage cliff at low charge levels than the IC expects, so the phone reads 25% on screen while the actual cell voltage has already dropped below the modem's minimum operating threshold. The CPU and radio draw a combined spike the cell cannot sustain at that state, and the phone shuts off. Run two full discharge-charge cycles without fast charging — by the end of the second cycle, the coulomb counter recalibrates and shutdowns stop. Confirm by checking that the phone shuts off at or below 5%.

Phone will not power on after the battery sat in storage

A cell stored below 2.5V triggers a BMS lockout — the protection circuit opens and refuses to pass current until voltage is recovered. Plugging in the charger may show no response at all for the first 10–20 minutes. Leave the phone connected to a wall charger (not a PC USB port) and wait — the charge IC trickle-charges the cell at a low current rate until voltage climbs above the BMS re-enable threshold of approximately 2.9V. Once that threshold is crossed, the BMS closes the circuit and the phone will power on normally.