Battery, Charging and Power Management
What this domain tests
Battery, Charging and Power Management tests Li-ion behaviour, charging circuits and safe power diagnosis.
Core rules
- Li-ion nominal is about 3.7–3.8 V, full charge 4.2–4.35 V, cutoff around 3.0 V. Charging is constant-current then constant-voltage.
- The protection board prevents overcharge, over-discharge and short circuit; the fuel gauge estimates charge; the charger IC regulates input current.
- Use the specified charger and cable. Measure voltage at the port, then at the battery connector, and note current draw under charge.
- A swollen, leaking or hot battery is unsafe: isolate it, do not puncture, and replace it.
- Never bypass protection or charge a frozen/over-discharged cell without proper procedure.
Worked example
A phone charges slowly. Measure the charger's output under load; if it collapses from 5 V to 4.3 V, the charger or cable is faulty. If the port receives 5 V but the battery current is only 0.2 A, inspect the port, charger IC and battery temperature signal. A high current with no charge rise suggests a faulty battery or fuel-gauge calibration. Calculate charging power: 5 V × 0.2 A = 1 W, far below a normal fast charge, so the fault is real. The reasoning follows power from source to battery.
Traps
Judging state of charge from voltage alone; using a cheap charger; measuring current with the meter in parallel; ignoring a swollen battery; assuming a charging IC fault before checking the cable and port.