MaxCom MM238 Replacement Battery 3.7V 1200mAh Li-ion

MaxCom MM238 — 3.7V Li-ion Replacement Battery (MM238)

This is a 3.7V, 1200mAh lithium-ion battery for the MaxCom MM238 mobile phone. It fits the MM238 directly, matching the original cell's voltage and connector. Dimensions are 60.00 × 43.80 × 4.50mm — confirm against your existing battery before ordering.

• MM238 cell fitment: The MM238 uses a compact single-cell 3.7V Li-ion pack with a low-current BMS suited to the phone's basic modem and display load. Voltage rail and connector position match the original — no modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MM238 platform. The BMS accepted charge from the phone's onboard charge IC without tripping, and the protection circuit held under sustained screen-on and call load.
• Fuel gauge recalibration on first use: On first use after installation, run one complete discharge-to-charge cycle without interruption. This lets the MM238's fuel gauge IC map the new cell's discharge curve and report accurate percentages from cycle two onward.

Sudden shutdown at 20–30% on the MM238 after a cell swap

A new Li-ion cell has a slightly different voltage-versus-capacity curve than the worn cell it replaces. The MM238's fuel gauge IC still holds the old curve in memory, so it reads 25% when the actual cell voltage is already close to the low-voltage cutoff. Under modem or screen load, current draw spikes and the cell voltage drops past the BMS cutoff instantly — the phone shuts off. One full discharge-charge cycle rewrites the reference curve. After that cycle, shutdowns at false percentages stop.

MM238 not powering on after the replacement battery sat in storage

Li-ion cells self-discharge during storage. If the cell voltage has dropped below approximately 2.5V, the BMS locks out to prevent damage — the phone will not respond to the power button or a standard charger. Connect the phone to a wall charger rated at 5V and leave it for 20–30 minutes without pressing anything. Most charge ICs apply a low-current trickle to recover a locked-out cell. If the charging indicator appears, continue a full charge before first use.